算法-直方图装水问题

public static void main(String[] args) {
//        int[] ints = {0,0,0,1,0,0};
        int[] ints = {2,1,5,1,2};
//        int[] ints = {5, 1, 1, 5};
//        int[] ints = {1, 3, 2, 4, 1};
        System.out.println(getWater(ints));
    }

    public static int getWater(int[] arr) {
        if (null == arr) {
            return 0;
        }
        int count = 0;
        for (int i = 0; i < arr.length; i++) {
            int leftMax = (i == 0) ? 0 : max(arr, 0, i);
            int rightMax = (i == arr.length - 1) ? 0 : max(arr, i + 1, arr.length);
            int max = Math.min(leftMax, rightMax);
            int water = max - arr[i];
            if (water > 0) {
                count += water;
            }
        }
        return count;
    }

    public static int max(int[] arr, int start, int end) {
        if (null == arr || start < 0 || end > arr.length || end < start) {
            return 0;
        }

        int max = arr[start];
        for (int i = start + 1; i < end; i++) {
            max = Math.max(max, arr[i]);
        }
        return max;
    }