diff --git a/problems/0042.接雨水.md b/problems/0042.接雨水.md
index 73d787b1..6d92d2b3 100644
--- a/problems/0042.接雨水.md
+++ b/problems/0042.接雨水.md
@@ -440,6 +440,33 @@ class Solution {
 }
 ```
 
+双指针优化
+```java
+class Solution {
+    public int trap(int[] height) {
+        if (height.length <= 2) {
+            return 0;
+        }
+        // 从两边向中间寻找最值
+        int maxLeft = height[0], maxRight = height[height.length - 1];
+        int l = 1, r = height.length - 2;
+        int res = 0;
+        while (l <= r) {
+            // 不确定上一轮是左边移动还是右边移动，所以两边都需更新最值
+            maxLeft = Math.max(maxLeft, height[l]);
+            maxRight = Math.max(maxRight, height[r]);
+            // 最值较小的一边所能装的水量已定，所以移动较小的一边。
+            if (maxLeft < maxRight) {
+                res += maxLeft - height[l ++];
+            } else {
+                res += maxRight - height[r --];
+            }
+        }
+        return res;
+    }
+}
+```
+
 单调栈法
 
 ```java