Update TrappingRainWater.cpp

TrappingRainWater/TrappingRainWater.cpp

@@ -1,58 +1,31 @@
-// O(n) time, O(n) space
 class Solution {
 public:
     int trap(int A[], int n) {
-        // Start typing your C/C++ solution below
-        // DO NOT write int main() function
-
-        int max_from_left[n];
-        int max_from_right[n];
-
-        max_from_left[0] = A[0];
-        for (int i = 1; i < n; i++)
-            max_from_left[i] = max(max_from_left[i-1], A[i]);
-
-        max_from_right[n-1] = A[n-1];
-        for (int i = n - 2; i >= 0; i--)
-            max_from_right[i] = max(max_from_right[i+1], A[i]);
-
-        int water = 0;
-        for (int i = 1; i < n - 1; i++) {
-            int min_height = min(max_from_left[i-1], max_from_right[i+1]);
-            if (min_height > A[i])
-                water += min_height - A[i];
-        }
-        return water;
-    }
-};
+        if(n<=1)
+			return 0;
+		int start = 0;
+		int end = n-1;
 
-// O(n) time, O(1) space
-class Solution {
-public:
-    int trap(int A[], int n) {
-        int maxh = 0;
-        int water = 0;
-        int temp = 0;
-        for (int i = 0; i < n; i++) {
-            if (A[i] <= maxh) {
-                temp += maxh - A[i];
-            } else {
-                maxh = A[i];
-                water += temp;
-                temp = 0;
-            }
-        }
-        maxh = 0;
-        temp = 0;
-        for (int i = n - 1; i >= 0; i--) {
-            if (A[i] < maxh) {
-                temp += maxh - A[i];
-            } else {
-                maxh = A[i];
-                water += temp;
-                temp = 0;
-            }
-        }
-        return water;
+		int leftMax = A[start];
+		int rightMax = A[end];
+
+		int capacity;
+		while(start < end){
+			if(leftMax <= rightMax){
+				if(A[start+1] < leftMax){
+					capacity += (leftMax - A[start+1]);
+				}else{
+					leftMax = A[start+1];
+				}
+				start++;				
+			}else{
+				if(A[end-1] < rightMax){
+					capacity += (rightMax - A[end-1]);
+				}else
+					rightMax = A[end-1];
+				end--;
+			}
+		}
+		return capacity;
     }
 };