42.接雨水

/**
 * @Classname CatchRain
 * @Description TODO
 * @Version 1.0.0
 * @Date 2021/11/2 9:20
 * @Created by DiTian
 */
public class CatchRain {
    public static void main(String[] args) {
        int[] height = new int[]{0,1,0,2,1,0,1,3,2,1,2,1};
        //动态规划实现
        //int total = trap1(height);
        //单调栈实现
        //int total = trap2(height);
        //双指针实现
        int total = trap3(height);
        System.out.println("最大雨水量："+total);
    }

    private static int trap3(int[] height) {
        int ans = 0;
        int left = 0,right = height.length-1;
        int leftMax = 0,rightMax = 0;
        while (left < right){
            leftMax = Math.max(leftMax,height[left]);
            rightMax = Math.max(rightMax,height[right]);
            if (height[left] < height[right]){
                ans += leftMax-height[left];
                left++;
            }else {
                ans += rightMax-height[right];
                right--;
            }
        }
        return ans;
    }

    private static int trap2(int[] height) {
        int ans = 0;
        Deque<Integer> stack = new LinkedList<Integer>();
        int n = height.length;
        for (int i = 0; i < n; i++) {
            while (!stack.isEmpty() && height[i] > height[stack.peek()]){
                int top = stack.pop(); //取出栈顶元素
                if (stack.isEmpty()) break;
                int left = stack.peek();
                int currWidth = i-left-1;
                int currHeight = Math.min(height[left],height[i])-height[top];
                ans += currWidth*currHeight;
            }
            stack.push(i);
        }
        return ans;
    }

    private static int trap1(int[] height) {
        int n = height.length;

        //1,记录左边最大高度
        int[] leftMaxArr = new int[n];
        leftMaxArr[0] = height[0];
        for (int i = 1; i < n; i++) {
            leftMaxArr[i] = Math.max(leftMaxArr[i-1],height[i]);
        }
        //2,记录右边最大高度
        int[] rightMaxArr = new int[n];
        rightMaxArr[n-1] = height[n-1];
        for (int i = n-2; i >= 0 ; i--) {
            rightMaxArr[i] = Math.max(rightMaxArr[i+1],height[i]);
        }
        //3,求雨水总量
        int ans = 0;
        for (int i = 0; i < n; i++) {
            ans += Math.min(leftMaxArr[i],rightMaxArr[i])-height[i];
        }
        return ans;

    }
}