42. 接雨水

public class Solution {
    // leetcode42，接雨水
    public int trap(int[] height) {
        int size = height.length;
        if (size <= 1) {
            return 0;
        }

        int[] lh = new int[size];
        int[] rh = new int[size];
        lh[0] = 0;
        for (int i = 1; i < size; i++) {
            lh[i] = Math.max(lh[i - 1], height[i-1]);
        }
        rh[size - 1] = 0;
        for (int i = size - 2; i >= 0; i--) {
            rh[i] = Math.max(rh[i + 1], height[i+1]);
        }

        int sum = 0;
        for (int i = 1; i <= size - 2; i++) {
            // 第i列可装雨水量为左边或右边最高度-当前列的高度：max(0, min(lh, rh) - curh)
            sum += Math.max(Math.min(lh[i], rh[i]) - height[i], 0);
        }
        return sum;
    }
}