diff --git a/src/main/java/g3401_3500/s3417_zigzag_grid_traversal_with_skip/Solution.java b/src/main/java/g3401_3500/s3417_zigzag_grid_traversal_with_skip/Solution.java
new file mode 100644
index 000000000..7863b5ae1
--- /dev/null
+++ b/src/main/java/g3401_3500/s3417_zigzag_grid_traversal_with_skip/Solution.java
@@ -0,0 +1,37 @@
+package g3401_3500.s3417_zigzag_grid_traversal_with_skip;
+
+// #Easy #Array #Matrix #Simulation #2025_01_15_Time_1_(100.00%)_Space_45.56_(84.25%)
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Solution {
+    public List<Integer> zigzagTraversal(int[][] grid) {
+        List<Integer> ans = new ArrayList<>();
+        int m = grid.length;
+        int n = grid[0].length;
+        int i = 0;
+        boolean flag = true;
+        boolean skip = false;
+        while (i < m) {
+            if (flag) {
+                for (int j = 0; j < n; j++) {
+                    if (!skip) {
+                        ans.add(grid[i][j]);
+                    }
+                    skip = !skip;
+                }
+            } else {
+                for (int j = n - 1; j >= 0; j--) {
+                    if (!skip) {
+                        ans.add(grid[i][j]);
+                    }
+                    skip = !skip;
+                }
+            }
+            flag = !flag;
+            i++;
+        }
+        return ans;
+    }
+}
diff --git a/src/main/java/g3401_3500/s3417_zigzag_grid_traversal_with_skip/readme.md b/src/main/java/g3401_3500/s3417_zigzag_grid_traversal_with_skip/readme.md
new file mode 100644
index 000000000..a652ca4a8
--- /dev/null
+++ b/src/main/java/g3401_3500/s3417_zigzag_grid_traversal_with_skip/readme.md
@@ -0,0 +1,54 @@
+3417\. Zigzag Grid Traversal With Skip
+
+Easy
+
+You are given an `m x n` 2D array `grid` of **positive** integers.
+
+Your task is to traverse `grid` in a **zigzag** pattern while skipping every **alternate** cell.
+
+Zigzag pattern traversal is defined as following the below actions:
+
+*   Start at the top-left cell `(0, 0)`.
+*   Move _right_ within a row until the end of the row is reached.
+*   Drop down to the next row, then traverse _left_ until the beginning of the row is reached.
+*   Continue **alternating** between right and left traversal until every row has been traversed.
+
+**Note** that you **must skip** every _alternate_ cell during the traversal.
+
+Return an array of integers `result` containing, **in order**, the value of the cells visited during the zigzag traversal with skips.
+
+**Example 1:**
+
+**Input:** grid = [[1,2],[3,4]]
+
+**Output:** [1,4]
+
+**Explanation:**
+
+**![](https://assets.leetcode.com/uploads/2024/11/23/4012_example0.png)**
+
+**Example 2:**
+
+**Input:** grid = [[2,1],[2,1],[2,1]]
+
+**Output:** [2,1,2]
+
+**Explanation:**
+
+![](https://assets.leetcode.com/uploads/2024/11/23/4012_example1.png)
+
+**Example 3:**
+
+**Input:** grid = [[1,2,3],[4,5,6],[7,8,9]]
+
+**Output:** [1,3,5,7,9]
+
+**Explanation:**
+
+![](https://assets.leetcode.com/uploads/2024/11/23/4012_example2.png)
+
+**Constraints:**
+
+*   `2 <= n == grid.length <= 50`
+*   `2 <= m == grid[i].length <= 50`
+*   `1 <= grid[i][j] <= 2500`
\ No newline at end of file
diff --git a/src/main/java/g3401_3500/s3418_maximum_amount_of_money_robot_can_earn/Solution.java b/src/main/java/g3401_3500/s3418_maximum_amount_of_money_robot_can_earn/Solution.java
new file mode 100644
index 000000000..a91076041
--- /dev/null
+++ b/src/main/java/g3401_3500/s3418_maximum_amount_of_money_robot_can_earn/Solution.java
@@ -0,0 +1,56 @@
+package g3401_3500.s3418_maximum_amount_of_money_robot_can_earn;
+
+// #Medium #Array #Dynamic_Programming #Matrix #2025_01_15_Time_12_(99.86%)_Space_72.43_(98.47%)
+
+public class Solution {
+    public int maximumAmount(int[][] coins) {
+        int m = coins.length;
+        int n = coins[0].length;
+        int[][] dp = new int[m][n];
+        int[][] dp1 = new int[m][n];
+        int[][] dp2 = new int[m][n];
+        dp[0][0] = coins[0][0];
+        for (int j = 1; j < n; j++) {
+            dp[0][j] = dp[0][j - 1] + coins[0][j];
+        }
+        for (int i = 1; i < m; i++) {
+            dp[i][0] = dp[i - 1][0] + coins[i][0];
+        }
+        for (int i = 1; i < m; i++) {
+            for (int j = 1; j < n; j++) {
+                dp[i][j] = Math.max(dp[i][j - 1], dp[i - 1][j]) + coins[i][j];
+            }
+        }
+        dp1[0][0] = Math.max(coins[0][0], 0);
+        for (int j = 1; j < n; j++) {
+            dp1[0][j] = Math.max(dp[0][j - 1], dp1[0][j - 1] + coins[0][j]);
+        }
+        for (int i = 1; i < m; i++) {
+            dp1[i][0] = Math.max(dp[i - 1][0], dp1[i - 1][0] + coins[i][0]);
+        }
+        for (int i = 1; i < m; i++) {
+            for (int j = 1; j < n; j++) {
+                dp1[i][j] =
+                        Math.max(
+                                Math.max(dp[i][j - 1], dp[i - 1][j]),
+                                Math.max(dp1[i][j - 1], dp1[i - 1][j]) + coins[i][j]);
+            }
+        }
+        dp2[0][0] = Math.max(coins[0][0], 0);
+        for (int j = 1; j < n; j++) {
+            dp2[0][j] = Math.max(dp1[0][j - 1], dp2[0][j - 1] + coins[0][j]);
+        }
+        for (int i = 1; i < m; i++) {
+            dp2[i][0] = Math.max(dp1[i - 1][0], dp2[i - 1][0] + coins[i][0]);
+        }
+        for (int i = 1; i < m; i++) {
+            for (int j = 1; j < n; j++) {
+                dp2[i][j] =
+                        Math.max(
+                                Math.max(dp1[i][j - 1], dp1[i - 1][j]),
+                                Math.max(dp2[i][j - 1], dp2[i - 1][j]) + coins[i][j]);
+            }
+        }
+        return dp2[m - 1][n - 1];
+    }
+}
diff --git a/src/main/java/g3401_3500/s3418_maximum_amount_of_money_robot_can_earn/readme.md b/src/main/java/g3401_3500/s3418_maximum_amount_of_money_robot_can_earn/readme.md
new file mode 100644
index 000000000..40f1fa1a0
--- /dev/null
+++ b/src/main/java/g3401_3500/s3418_maximum_amount_of_money_robot_can_earn/readme.md
@@ -0,0 +1,54 @@
+3418\. Maximum Amount of Money Robot Can Earn
+
+Medium
+
+You are given an `m x n` grid. A robot starts at the top-left corner of the grid `(0, 0)` and wants to reach the bottom-right corner `(m - 1, n - 1)`. The robot can move either right or down at any point in time.
+
+The grid contains a value `coins[i][j]` in each cell:
+
+*   If `coins[i][j] >= 0`, the robot gains that many coins.
+*   If `coins[i][j] < 0`, the robot encounters a robber, and the robber steals the **absolute** value of `coins[i][j]` coins.
+
+The robot has a special ability to **neutralize robbers** in at most **2 cells** on its path, preventing them from stealing coins in those cells.
+
+**Note:** The robot's total coins can be negative.
+
+Return the **maximum** profit the robot can gain on the route.
+
+**Example 1:**
+
+**Input:** coins = [[0,1,-1],[1,-2,3],[2,-3,4]]
+
+**Output:** 8
+
+**Explanation:**
+
+An optimal path for maximum coins is:
+
+1.  Start at `(0, 0)` with `0` coins (total coins = `0`).
+2.  Move to `(0, 1)`, gaining `1` coin (total coins = `0 + 1 = 1`).
+3.  Move to `(1, 1)`, where there's a robber stealing `2` coins. The robot uses one neutralization here, avoiding the robbery (total coins = `1`).
+4.  Move to `(1, 2)`, gaining `3` coins (total coins = `1 + 3 = 4`).
+5.  Move to `(2, 2)`, gaining `4` coins (total coins = `4 + 4 = 8`).
+
+**Example 2:**
+
+**Input:** coins = [[10,10,10],[10,10,10]]
+
+**Output:** 40
+
+**Explanation:**
+
+An optimal path for maximum coins is:
+
+1.  Start at `(0, 0)` with `10` coins (total coins = `10`).
+2.  Move to `(0, 1)`, gaining `10` coins (total coins = `10 + 10 = 20`).
+3.  Move to `(0, 2)`, gaining another `10` coins (total coins = `20 + 10 = 30`).
+4.  Move to `(1, 2)`, gaining the final `10` coins (total coins = `30 + 10 = 40`).
+
+**Constraints:**
+
+*   `m == coins.length`
+*   `n == coins[i].length`
+*   `1 <= m, n <= 500`
+*   `-1000 <= coins[i][j] <= 1000`
\ No newline at end of file
diff --git a/src/main/java/g3401_3500/s3419_minimize_the_maximum_edge_weight_of_graph/Solution.java b/src/main/java/g3401_3500/s3419_minimize_the_maximum_edge_weight_of_graph/Solution.java
new file mode 100644
index 000000000..12669cec0
--- /dev/null
+++ b/src/main/java/g3401_3500/s3419_minimize_the_maximum_edge_weight_of_graph/Solution.java
@@ -0,0 +1,84 @@
+package g3401_3500.s3419_minimize_the_maximum_edge_weight_of_graph;
+
+// #Medium #Binary_Search #Graph #Shortest_Path #Depth_First_Search #Breadth_First_Search
+// #2025_01_15_Time_64_(99.28%)_Space_110.17_(57.63%)
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.LinkedList;
+import java.util.Queue;
+
+@SuppressWarnings({"unchecked", "unused", "java:S1172"})
+public class Solution {
+    private ArrayList<ArrayList<Pair>> revadj;
+
+    private static class Pair {
+        int node;
+        int weight;
+
+        public Pair(int node, int weight) {
+            this.node = node;
+            this.weight = weight;
+        }
+    }
+
+    public int minMaxWeight(int n, int[][] edges, int threshold) {
+        ArrayList<ArrayList<Pair>> adj = new ArrayList<>();
+        revadj = new ArrayList<>();
+        for (int i = 0; i <= n + 1; i++) {
+            adj.add(new ArrayList<>());
+            revadj.add(new ArrayList<>());
+        }
+        for (int[] edge : edges) {
+            int u = edge[0];
+            int v = edge[1];
+            int wt = edge[2];
+            adj.get(u).add(new Pair(v, wt));
+            revadj.get(v).add(new Pair(u, wt));
+        }
+        if (!check(n)) {
+            return -1;
+        }
+        int[] dist = new int[n + 1];
+        Arrays.fill(dist, (int) (1e9));
+        dist[0] = 0;
+        Queue<Pair> q = new LinkedList<>();
+        q.offer(new Pair(0, 0));
+        while (!q.isEmpty()) {
+            int u = q.peek().node;
+            int currMax = q.peek().weight;
+            q.poll();
+            for (int i = 0; i < revadj.get(u).size(); i++) {
+                int v = revadj.get(u).get(i).node;
+                int wt = revadj.get(u).get(i).weight;
+                if (dist[v] > Math.max(wt, currMax)) {
+                    dist[v] = Math.max(wt, currMax);
+                    q.offer(new Pair(v, dist[v]));
+                }
+            }
+        }
+        int maxi = dist[0];
+        for (int i = 0; i < n; i++) {
+            maxi = Math.max(maxi, dist[i]);
+        }
+        return maxi;
+    }
+
+    private boolean check(int n) {
+        int[] vis = new int[n];
+        ArrayList<Integer> nodes = new ArrayList<>();
+        dfs(0, vis, nodes);
+        return nodes.size() == n;
+    }
+
+    private void dfs(int u, int[] vis, ArrayList<Integer> nodes) {
+        nodes.add(u);
+        vis[u] = 1;
+        for (int i = 0; i < revadj.get(u).size(); i++) {
+            int v = revadj.get(u).get(i).node;
+            if (vis[v] == 0) {
+                dfs(v, vis, nodes);
+            }
+        }
+    }
+}
diff --git a/src/main/java/g3401_3500/s3419_minimize_the_maximum_edge_weight_of_graph/readme.md b/src/main/java/g3401_3500/s3419_minimize_the_maximum_edge_weight_of_graph/readme.md
new file mode 100644
index 000000000..90c5eba33
--- /dev/null
+++ b/src/main/java/g3401_3500/s3419_minimize_the_maximum_edge_weight_of_graph/readme.md
@@ -0,0 +1,64 @@
+3419\. Minimize the Maximum Edge Weight of Graph
+
+Medium
+
+You are given two integers, `n` and `threshold`, as well as a **directed** weighted graph of `n` nodes numbered from 0 to `n - 1`. The graph is represented by a **2D** integer array `edges`, where <code>edges[i] = [A<sub>i</sub>, B<sub>i</sub>, W<sub>i</sub>]</code> indicates that there is an edge going from node <code>A<sub>i</sub></code> to node <code>B<sub>i</sub></code> with weight <code>W<sub>i</sub></code>.
+
+You have to remove some edges from this graph (possibly **none**), so that it satisfies the following conditions:
+
+*   Node 0 must be reachable from all other nodes.
+*   The **maximum** edge weight in the resulting graph is **minimized**.
+*   Each node has **at most** `threshold` outgoing edges.
+
+Return the **minimum** possible value of the **maximum** edge weight after removing the necessary edges. If it is impossible for all conditions to be satisfied, return -1.
+
+**Example 1:**
+
+**Input:** n = 5, edges = [[1,0,1],[2,0,2],[3,0,1],[4,3,1],[2,1,1]], threshold = 2
+
+**Output:** 1
+
+**Explanation:**
+
+![](https://assets.leetcode.com/uploads/2024/12/09/s-1.png)
+
+Remove the edge `2 -> 0`. The maximum weight among the remaining edges is 1.
+
+**Example 2:**
+
+**Input:** n = 5, edges = [[0,1,1],[0,2,2],[0,3,1],[0,4,1],[1,2,1],[1,4,1]], threshold = 1
+
+**Output:** \-1
+
+**Explanation:**
+
+It is impossible to reach node 0 from node 2.
+
+**Example 3:**
+
+**Input:** n = 5, edges = [[1,2,1],[1,3,3],[1,4,5],[2,3,2],[3,4,2],[4,0,1]], threshold = 1
+
+**Output:** 2
+
+**Explanation:**
+
+![](https://assets.leetcode.com/uploads/2024/12/09/s2-1.png)
+
+Remove the edges `1 -> 3` and `1 -> 4`. The maximum weight among the remaining edges is 2.
+
+**Example 4:**
+
+**Input:** n = 5, edges = [[1,2,1],[1,3,3],[1,4,5],[2,3,2],[4,0,1]], threshold = 1
+
+**Output:** \-1
+
+**Constraints:**
+
+*   <code>2 <= n <= 10<sup>5</sup></code>
+*   `1 <= threshold <= n - 1`
+*   <code>1 <= edges.length <= min(10<sup>5</sup>, n * (n - 1) / 2).</code>
+*   `edges[i].length == 3`
+*   <code>0 <= A<sub>i</sub>, B<sub>i</sub> < n</code>
+*   <code>A<sub>i</sub> != B<sub>i</sub></code>
+*   <code>1 <= W<sub>i</sub> <= 10<sup>6</sup></code>
+*   There **may be** multiple edges between a pair of nodes, but they must have unique weights.
\ No newline at end of file
diff --git a/src/main/java/g3401_3500/s3420_count_non_decreasing_subarrays_after_k_operations/Solution.java b/src/main/java/g3401_3500/s3420_count_non_decreasing_subarrays_after_k_operations/Solution.java
new file mode 100644
index 000000000..28780ea83
--- /dev/null
+++ b/src/main/java/g3401_3500/s3420_count_non_decreasing_subarrays_after_k_operations/Solution.java
@@ -0,0 +1,38 @@
+package g3401_3500.s3420_count_non_decreasing_subarrays_after_k_operations;
+
+// #Hard #Array #Two_Pointers #Stack #Monotonic_Stack #Queue #Segment_Tree #Monotonic_Queue
+// #2025_01_15_Time_29_(83.94%)_Space_62.04_(56.93%)
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+
+public class Solution {
+    public long countNonDecreasingSubarrays(int[] nums, long k) {
+        int n = nums.length;
+        for (int i = 0; i < n / 2; ++i) {
+            int temp = nums[i];
+            nums[i] = nums[n - 1 - i];
+            nums[n - 1 - i] = temp;
+        }
+        long res = 0;
+        Deque<Integer> q = new ArrayDeque<>();
+        int i = 0;
+        for (int j = 0; j < nums.length; ++j) {
+            while (!q.isEmpty() && nums[q.peekLast()] < nums[j]) {
+                int r = q.pollLast();
+                int l = q.isEmpty() ? i - 1 : q.peekLast();
+                k -= (long) (r - l) * (nums[j] - nums[r]);
+            }
+            q.addLast(j);
+            while (k < 0) {
+                k += nums[q.peekFirst()] - nums[i];
+                if (q.peekFirst() == i) {
+                    q.pollFirst();
+                }
+                ++i;
+            }
+            res += j - i + 1;
+        }
+        return res;
+    }
+}
diff --git a/src/main/java/g3401_3500/s3420_count_non_decreasing_subarrays_after_k_operations/readme.md b/src/main/java/g3401_3500/s3420_count_non_decreasing_subarrays_after_k_operations/readme.md
new file mode 100644
index 000000000..46169b39e
--- /dev/null
+++ b/src/main/java/g3401_3500/s3420_count_non_decreasing_subarrays_after_k_operations/readme.md
@@ -0,0 +1,39 @@
+3420\. Count Non-Decreasing Subarrays After K Operations
+
+Hard
+
+You are given an array `nums` of `n` integers and an integer `k`.
+
+For each subarray of `nums`, you can apply **up to** `k` operations on it. In each operation, you increment any element of the subarray by 1.
+
+**Note** that each subarray is considered independently, meaning changes made to one subarray do not persist to another.
+
+Return the number of subarrays that you can make **non-decreasing** after performing at most `k` operations.
+
+An array is said to be **non-decreasing** if each element is greater than or equal to its previous element, if it exists.
+
+**Example 1:**
+
+**Input:** nums = [6,3,1,2,4,4], k = 7
+
+**Output:** 17
+
+**Explanation:**
+
+Out of all 21 possible subarrays of `nums`, only the subarrays `[6, 3, 1]`, `[6, 3, 1, 2]`, `[6, 3, 1, 2, 4]` and `[6, 3, 1, 2, 4, 4]` cannot be made non-decreasing after applying up to k = 7 operations. Thus, the number of non-decreasing subarrays is `21 - 4 = 17`.
+
+**Example 2:**
+
+**Input:** nums = [6,3,1,3,6], k = 4
+
+**Output:** 12
+
+**Explanation:**
+
+The subarray `[3, 1, 3, 6]` along with all subarrays of `nums` with three or fewer elements, except `[6, 3, 1]`, can be made non-decreasing after `k` operations. There are 5 subarrays of a single element, 4 subarrays of two elements, and 2 subarrays of three elements except `[6, 3, 1]`, so there are `1 + 5 + 4 + 2 = 12` subarrays that can be made non-decreasing.
+
+**Constraints:**
+
+*   <code>1 <= nums.length <= 10<sup>5</sup></code>
+*   <code>1 <= nums[i] <= 10<sup>9</sup></code>
+*   <code>1 <= k <= 10<sup>9</sup></code>
\ No newline at end of file
diff --git a/src/test/java/g3401_3500/s3417_zigzag_grid_traversal_with_skip/SolutionTest.java b/src/test/java/g3401_3500/s3417_zigzag_grid_traversal_with_skip/SolutionTest.java
new file mode 100644
index 000000000..ecd183508
--- /dev/null
+++ b/src/test/java/g3401_3500/s3417_zigzag_grid_traversal_with_skip/SolutionTest.java
@@ -0,0 +1,30 @@
+package g3401_3500.s3417_zigzag_grid_traversal_with_skip;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+class SolutionTest {
+    @Test
+    void zigzagTraversal() {
+        assertThat(
+                new Solution().zigzagTraversal(new int[][] {{1, 2}, {3, 4}}),
+                equalTo(List.of(1, 4)));
+    }
+
+    @Test
+    void zigzagTraversal2() {
+        assertThat(
+                new Solution().zigzagTraversal(new int[][] {{2, 1}, {2, 1}, {2, 1}}),
+                equalTo(List.of(2, 1, 2)));
+    }
+
+    @Test
+    void zigzagTraversal3() {
+        assertThat(
+                new Solution().zigzagTraversal(new int[][] {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}}),
+                equalTo(List.of(1, 3, 5, 7, 9)));
+    }
+}
diff --git a/src/test/java/g3401_3500/s3418_maximum_amount_of_money_robot_can_earn/SolutionTest.java b/src/test/java/g3401_3500/s3418_maximum_amount_of_money_robot_can_earn/SolutionTest.java
new file mode 100644
index 000000000..d8af0f9d0
--- /dev/null
+++ b/src/test/java/g3401_3500/s3418_maximum_amount_of_money_robot_can_earn/SolutionTest.java
@@ -0,0 +1,22 @@
+package g3401_3500.s3418_maximum_amount_of_money_robot_can_earn;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+class SolutionTest {
+    @Test
+    void maximumAmount() {
+        assertThat(
+                new Solution().maximumAmount(new int[][] {{0, 1, -1}, {1, -2, 3}, {2, -3, 4}}),
+                equalTo(8));
+    }
+
+    @Test
+    void maximumAmount2() {
+        assertThat(
+                new Solution().maximumAmount(new int[][] {{10, 10, 10}, {10, 10, 10}}),
+                equalTo(40));
+    }
+}
diff --git a/src/test/java/g3401_3500/s3419_minimize_the_maximum_edge_weight_of_graph/SolutionTest.java b/src/test/java/g3401_3500/s3419_minimize_the_maximum_edge_weight_of_graph/SolutionTest.java
new file mode 100644
index 000000000..8ee38965a
--- /dev/null
+++ b/src/test/java/g3401_3500/s3419_minimize_the_maximum_edge_weight_of_graph/SolutionTest.java
@@ -0,0 +1,56 @@
+package g3401_3500.s3419_minimize_the_maximum_edge_weight_of_graph;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+class SolutionTest {
+    @Test
+    void minMaxWeight() {
+        assertThat(
+                new Solution()
+                        .minMaxWeight(
+                                5,
+                                new int[][] {{1, 0, 1}, {2, 0, 2}, {3, 0, 1}, {4, 3, 1}, {2, 1, 1}},
+                                2),
+                equalTo(1));
+    }
+
+    @Test
+    void minMaxWeight2() {
+        assertThat(
+                new Solution()
+                        .minMaxWeight(
+                                5,
+                                new int[][] {
+                                    {0, 1, 1}, {0, 2, 2}, {0, 3, 1}, {0, 4, 1}, {1, 2, 1}, {1, 4, 1}
+                                },
+                                1),
+                equalTo(-1));
+    }
+
+    @Test
+    void minMaxWeight3() {
+        assertThat(
+                new Solution()
+                        .minMaxWeight(
+                                5,
+                                new int[][] {
+                                    {1, 2, 1}, {1, 3, 3}, {1, 4, 5}, {2, 3, 2}, {3, 4, 2}, {4, 0, 1}
+                                },
+                                1),
+                equalTo(2));
+    }
+
+    @Test
+    void minMaxWeight4() {
+        assertThat(
+                new Solution()
+                        .minMaxWeight(
+                                5,
+                                new int[][] {{1, 2, 1}, {1, 3, 3}, {1, 4, 5}, {2, 3, 2}, {4, 0, 1}},
+                                1),
+                equalTo(-1));
+    }
+}
diff --git a/src/test/java/g3401_3500/s3420_count_non_decreasing_subarrays_after_k_operations/SolutionTest.java b/src/test/java/g3401_3500/s3420_count_non_decreasing_subarrays_after_k_operations/SolutionTest.java
new file mode 100644
index 000000000..5a71b177f
--- /dev/null
+++ b/src/test/java/g3401_3500/s3420_count_non_decreasing_subarrays_after_k_operations/SolutionTest.java
@@ -0,0 +1,22 @@
+package g3401_3500.s3420_count_non_decreasing_subarrays_after_k_operations;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+class SolutionTest {
+    @Test
+    void countNonDecreasingSubarrays() {
+        assertThat(
+                new Solution().countNonDecreasingSubarrays(new int[] {6, 3, 1, 2, 4, 4}, 7),
+                equalTo(17L));
+    }
+
+    @Test
+    void countNonDecreasingSubarrays2() {
+        assertThat(
+                new Solution().countNonDecreasingSubarrays(new int[] {6, 3, 1, 3, 6}, 4),
+                equalTo(12L));
+    }
+}