Merge pull request #740 from andywang0607/454_rust

增加0454.四数相加II Rust語言版本

problems/0454.四数相加II.md

@@ -282,6 +282,31 @@ func fourSumCount(_ nums1: [Int], _ nums2: [Int], _ nums3: [Int], _ nums4: [Int]
 }
 ```
 
+Rust：
+```rust
+use std::collections::HashMap;
+impl Solution {
+    pub fn four_sum_count(nums1: Vec<i32>, nums2: Vec<i32>, nums3: Vec<i32>, nums4: Vec<i32>) -> i32 {
+        let mut umap:HashMap<i32, i32> = HashMap::new();
+        for num1 in &nums1 {
+            for num2 in &nums2 {
+                *umap.entry(num1 + num2).or_insert(0) += 1;
+            }
+        }
+        
+        let mut count = 0;
+        
+        for num3 in &nums3 {
+            for num4 in &nums4 {
+                let target:i32 = - (num3 + num4);
+                count += umap.get(&target).unwrap_or(&0);          
+            }
+        }
+        
+        count
+     }
+}
+```
 
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 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)