1

Author: Ainevsia

notes/src/day7/lc383.md

@@ -32,4 +32,6 @@ impl Solution {
 }
 ```
 
-## 学习感想
+## 学习感想
+
+普通hashmap 的使用

notes/src/day7/lc454.md

@@ -75,4 +75,34 @@ impl Solution {
         res as i32
     }
 }
+```
+
+
+
+
+
+```rust
+struct Solution {}
+
+impl Solution {
+    pub fn four_sum_count(nums1: Vec<i32>, nums2: Vec<i32>, nums3: Vec<i32>, nums4: Vec<i32>) -> i32 {
+        use std::collections::HashMap;
+        let mut map: HashMap<i32, usize> = HashMap::new();
+        for a in nums1 {
+            for &b in nums2.iter() {
+                map.entry(a + b)
+                    .and_modify(|x| *x += 1usize)
+                    .or_insert(1usize);
+            }
+        }
+        let mut res: usize = 0usize;
+        for c in nums3 {
+            for &d in nums4.iter() {
+                map.entry(0i32 - c - d)
+                    .and_modify(|&mut x| res += x);
+            }
+        }
+        res as i32
+    }
+}
 ```