LeetCode Trapping Rain Water

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it is able to trap after raining.

For example,
Given

[0,1,0,2,1,0,1,3,2,1,2,1]

, return

6

.



The above elevation map is represented by array [0,1,0,2,1,0,1,3,2,1,2,1]. In this case, 6 units of rain water (blue section) are being trapped. Thanks Marcos for contributing this image!

找到最长的那块木板，假设其下标为maxIdx。

分别从左侧和右侧向其逼近。

在左侧逼近过程中：



右侧逼近过程与左侧相似。

public class Solution {
public int trap(int[] A) {
if (A.length<3) {
return 0;
}
int len=A.length;
int maxIndex=0;
//找出最大值的下标
for (int i = 0; i < len; i++) {
if (A[i]>A[maxIndex]) {
maxIndex=i;
}
}

int leftMax=0;
int rightMax=0;
int water=0;
for (int i = 0; i < maxIndex; i++) {
if (leftMax>A[i]) {
water=water+leftMax-A[i];
}else {
leftMax=A[i];
}
}

for (int i = len-1; i > maxIndex; i--) {
if (rightMax>A[i]) {
water=water+rightMax-A[i];
}else {
rightMax=A[i];
}
}
return water;
}
}