Update 42-trapping-rain-water.js

Author: everthis

42-trapping-rain-water.js

@@ -44,3 +44,37 @@ const trap = function(height) {
   }
   return res
 }
+
+// another
+
+/**
+ * @param {number[]} height
+ * @return {number}
+ */
+const trap = function(height) {
+  const len = height.length
+  if(len === 0) return 0
+  let left = 0
+  let right = len - 1
+  let leftMax = 0
+  let rightMax = 0
+  let res = 0
+  while(left < right) {
+    if(height[left] < height[right]) {
+      if(height[left] <= leftMax) {
+        res += leftMax - height[left]
+      } else {
+        leftMax = height[left]
+      }
+      left++
+    } else {
+      if(height[right] <= rightMax) {
+         res += rightMax - height[right]
+      } else {
+        rightMax = height[right]
+      }
+      right--
+    }
+  }
+  return res
+};