添加 0027.移除元素.md Dart相向双指针法

problems/0027.移除元素.md

@@ -476,6 +476,32 @@ public class Solution {
 }
 ```
 
+###Dart:
+```dart
+int removeElement(List<int> nums, int val) {
+    //相向双指针法
+    var left = 0;
+    var right = nums.length - 1;
+    while (left <= right) {
+	//寻找左侧的val，将其被右侧非val覆盖
+        if (nums[left] == val) {
+            while (nums[right] == val&&left<=right) {
+                right--;
+            if (right < 0) {
+                return 0;
+        }
+      }
+      nums[left] = nums[right--];
+    } else {
+      left++;
+    }
+  }
+  //覆盖后可以将0至left部分视为所需部分
+  return left;
+}
+
+```
+
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