Problem: 根据所给数组的值，按照上图的示意图。求解积水最大体积。
首先对所给数组进行遍历操作，求出最大高度所对应的下标为maxIndex
之后从左向右进行遍历，设置左边高度为leftMax 并初始化为 height[0],从i==1到i==maxIndex进行遍历。不断更新water，以及leftMax
当height[I]小于leftMax时，water += leftMax - height
当height[i]大于leftMax时，leftMax = height[I]
之后从i==height.length - 2到下标 I == maxIndex进行遍历操作 初始化rightMax = height[height.length-1]
当height[I]小于rightMax时，water+=rightMax - height[I]
当height[I]大于rightMax时，rightMax = height[I]
函数结果返回water
参考代码：
package leetcode_50; /***
*
* @author pengfei_zheng
* 求积水的体积
*/
public class Solution42 {
public static int trap(int[] height) {
if (height.length <= 2) return 0;
int max = -1;
int maxIndex = 0;
for (int i = 0; i < height.length; i++) {
if (height[i] > max) {
max = height[i];
maxIndex = i;
}
} int leftMax = height[0];
int water = 0;
for (int i = 1; i < maxIndex; i++) {
if (height[i] > leftMax) {
leftMax = height[i];
} else {
water += leftMax - height[i];
}
} int rightMax = height[height.length - 1];
for (int i= height.length - 2; i > maxIndex; i--) {
if (height[i] > rightMax) {
rightMax = height[i];
} else {
water += rightMax - height[i];
}
} return water;
}
public static void main(String[]args){
// int []height={0,1,0,2,1,0,1,3,2,1,2,1};
int []height={10,0,11,0,10};
System.out.println(trap(height));
}
}