Update readme.md

Co-Authored-By: Antim-IWP <203163676+Antim-IWP@users.noreply.github.com>
Co-Authored-By: Shiwangi Srivastava <174641070+IamShiwangi@users.noreply.github.com>

Author: 3 people

Solution/1372. Longest ZigZag Path in a Binary Tree/readme.md

@@ -0,0 +1,188 @@
+Sure! Here's the full `README.md` in the LeetCode-style format, exactly like in the `doocs/leetcode` GitHub repo, for **1372. Longest ZigZag Path in a Binary Tree**:
+
+---
+
+```markdown
+# [1372. Longest ZigZag Path in a Binary Tree](https://leetcode.com/problems/longest-zigzag-path-in-a-binary-tree)
+
+## Description
+
+You are given the `root` of a binary tree.
+
+A ZigZag path for a binary tree is defined as follows:
+
+- Choose **any** node in the binary tree and a direction (right or left).
+- If the current direction is right, move to the right child of the current node; otherwise, move to the left child.
+- Change the direction from right to left or from left to right.
+- Repeat the second and third steps until you can't move in the tree.
+
+The ZigZag length is defined as the number of nodes visited - 1. (A single node has a length of 0).
+
+Return _the longest **ZigZag** path contained in that tree_.
+
+## Examples
+
+**Example 1:**
+
+![example1](https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/1300-1399/1372.Longest%20ZigZag%20Path%20in%20a%20Binary%20Tree/images/sample_1_1702.png)
+
+```
+Input: root = [1,null,1,1,1,null,null,1,1,null,1,null,null,null,1]
+Output: 3
+Explanation: Longest ZigZag path in blue nodes (right -> left -> right).
+```
+
+**Example 2:**
+
+![example2](https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/1300-1399/1372.Longest%20ZigZag%20Path%20in%20a%20Binary%20Tree/images/sample_2_1702.png)
+
+```
+Input: root = [1,1,1,null,1,null,null,1,1,null,1]
+Output: 4
+Explanation: Longest ZigZag path in blue nodes (left -> right -> left -> right).
+```
+
+**Example 3:**
+
+```
+Input: root = [1]
+Output: 0
+```
+
+## Constraints
+
+- The number of nodes in the tree is in the range `[1, 5 * 10^4]`.
+- `1 <= Node.val <= 100`
+
+## Solutions
+
+### Python3
+
+```python
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    def longestZigZag(self, root: TreeNode) -> int:
+        def dfs(root, l, r):
+            if root is None:
+                return
+            nonlocal ans
+            ans = max(ans, l, r)
+            dfs(root.left, r + 1, 0)
+            dfs(root.right, 0, l + 1)
+
+        ans = 0
+        dfs(root, 0, 0)
+        return ans
+```
+
+### Java
+
+```java
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+class Solution {
+    private int ans;
+
+    public int longestZigZag(TreeNode root) {
+        dfs(root, 0, 0);
+        return ans;
+    }
+
+    private void dfs(TreeNode root, int l, int r) {
+        if (root == null) {
+            return;
+        }
+        ans = Math.max(ans, Math.max(l, r));
+        dfs(root.left, r + 1, 0);
+        dfs(root.right, 0, l + 1);
+    }
+}
+```
+
+### C++
+
+```cpp
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+    int ans = 0;
+
+    int longestZigZag(TreeNode* root) {
+        dfs(root, 0, 0);
+        return ans;
+    }
+
+    void dfs(TreeNode* root, int l, int r) {
+        if (!root) return;
+        ans = max(ans, max(l, r));
+        dfs(root->left, r + 1, 0);
+        dfs(root->right, 0, l + 1);
+    }
+};
+```
+
+### Go
+
+```go
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+func longestZigZag(root *TreeNode) int {
+	ans := 0
+	var dfs func(root *TreeNode, l, r int)
+	dfs = func(root *TreeNode, l, r int) {
+		if root == nil {
+			return
+		}
+		ans = max(ans, max(l, r))
+		dfs(root.Left, r+1, 0)
+		dfs(root.Right, 0, l+1)
+	}
+	dfs(root, 0, 0)
+	return ans
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
+```
+
+---
+
+Let me know if you want this in other languages or with a visual diagram too!