Update 42.trapping-rain-water.md

Author: daydaygo

problems/42.trapping-rain-water.md

@@ -182,7 +182,7 @@ int trap(vector<int>& heights)
 
 ### 代码
 
-代码支持 Python3，C++:
+代码支持 Python3，C++, Go:
 
 ```python
 class Solution:
@@ -232,6 +232,70 @@ public:
 };
 ```
 
+```go
+func trap(height []int) int {
+    if len(height) == 0 {
+        return 0
+    }
+
+    l, r := 0, len(height)-1
+    lMax, rMax := height[l], height[r]
+    ans := 0
+    for l < r {
+        if height[l] < height[r] {
+            if height[l] < lMax {
+                ans += lMax - height[l]
+            } else {
+                lMax = height[l]
+            }
+            l++
+        } else {
+            if height[r] < rMax {
+                ans += rMax - height[r]
+            } else {
+                rMax = height[r]
+            }
+            r--
+        }
+    }
+    return ans
+}
+```
+
+```php
+class Solution
+{
+
+    /**
+     * @param Integer[] $height
+     * @return Integer
+     */
+    function trap($height)
+    {
+        $n = count($height);
+        if (!$n) return 0;
+
+        $l = 0;
+        $l_max = $height[$l];
+        $r = $n - 1;
+        $r_max = $height[$r];
+        $ans = 0;
+        while ($l < $r) {
+            if ($height[$l] < $height[$r]) {
+                if ($height[$l] < $l_max) $ans += $l_max - $height[$l];
+                else $l_max = $height[$l];
+                $l++;
+            } else {
+                if ($height[$r] < $r_max) $ans += $r_max-$height[$r];
+                else $r_max = $height[$r];
+                $r--;
+            }
+        }
+        return $ans;
+    }
+}
+```
+
 **复杂度分析**
 
 - 时间复杂度：$O(N)$