题解 | 接雨水问题

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * max water
     * @param arr int整型一维数组 the array
     * @return long长整型
     */
    public long maxWater (int[] arr) {
        int[] leftMax = new int[arr.length];
        int[] rightMax = new int[arr.length];
        leftMax[0] = 0;
        for (int i = 1; i < arr.length; i++) {
            leftMax[i] = Math.max(leftMax[i - 1], arr[i - 1]);
        }
        rightMax[arr.length - 1] = 0;
        for (int i = arr.length - 2; i >= 0; i--) {
            rightMax[i] = Math.max(rightMax[i + 1], arr[i + 1]);
        }
        int sum = 0;
        for (int i = 1; i < arr.length - 1; i++) {
            int min = Math.min(leftMax[i], rightMax[i]);
            if (arr[i] < min) {
                sum += min - arr[i];
            }
        }
        return sum;
    }
}