两指针（7）

原题：

/** * Created by gouthamvidyapradhan on 08/03/2017. * 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. * <p> * For example, * Given [0,1,0,2,1,0,1,3,2,1,2,1], return 6. */

答案：

public class TrappingRainWater {    /**     * Main method     *     * @param args     * @throws Exception     */    public static void main(String[] args) throws Exception {        int[] height = {0, 1, 0, 2, 1, 0, 1, 3, 2, 1, 2, 1};        System.out.println(new TrappingRainWater().trap(height));    }    private int trap(int[] height) {        if (height.length == 0) return 0;        int[] left = new int[height.length];        int[] right = new int[height.length];        int max = 0;        left[0] = 0;        right[height.length - 1] = 0;        int total = 0;        for (int i = 1, l = height.length; i < l; i++) {            left[i] = Math.max(max, height[i - 1]);            max = left[i];        }        max = 0;        for (int i = height.length - 2; i >= 0; i--) {            right[i] = Math.max(max, height[i + 1]);            max = right[i];        }        for (int i = 0, l = height.length; i < l; i++) {            int min = Math.min(left[i], right[i]);            if (min > height[i]) {                total += (min - height[i]);            }        }        return total;    }}