代码随想录算法刷题训练营day49：LeetCode(42)接雨水、LeetCode(84)柱状图中最大的矩形

LeetCode(42)接雨水
题目

代码

import java.util.Stack;

class Solution {
    public int trap(int[] height) {
        //用单调栈进行操作
        int sum=0;
        Stack<Integer> stack=new Stack<>();
        for(int i=0;i<height.length;i++){
            if(stack.isEmpty()){
                stack.push(i);
            }else{
                while(!stack.isEmpty()&&height[i]>height[stack.peek()]){
                    int maxRight=i;
                    int middle=stack.peek();
                    stack.pop();
                    if(!stack.isEmpty()){
                        int maxLeft=stack.peek();
                        //计算面积
                        int tempHeight=0;
                        if(height[maxRight]>height[maxLeft]){
                            tempHeight=height[maxLeft];    
                        }else{
                            tempHeight=height[maxRight];
                        }
                        sum=sum+(tempHeight-height[middle])*(maxRight-maxLeft-1);//这里是减1
                    }
                }
                stack.push(i);
            }
        }
        return sum;

    }
}

LeetCode(84)柱状图中最大的矩形
题目

代码

import java.util.Stack;

class Solution {
    public int largestRectangleArea(int[] heights) {
        int maxArea=0;
        //最大面积，单调递减栈+首尾得增加两个0
        int[] dateHeight=new int[heights.length+2];
        dateHeight[0]=0;
        dateHeight[dateHeight.length-1]=0;
        for(int i=0;i<heights.length;i++){
            dateHeight[i+1]=heights[i];
        }
        Stack<Integer> stack=new Stack<>();//单调递减栈
        for(int i=0;i<dateHeight.length;i++){
            if(stack.isEmpty()){
                stack.push(i);
            }else{
                while (!stack.isEmpty()&&dateHeight[i]<dateHeight[stack.peek()]) {
                    int rightMin=i;
                    int mid=stack.peek();
                    stack.pop();
                    if(!stack.isEmpty()){
                        int leftMin=stack.peek();
                        if((rightMin-leftMin-1)*dateHeight[mid]>maxArea){
                            maxArea=(rightMin-leftMin-1)*dateHeight[mid];
                        }
                    }
                    
                }
                stack.push(i);
            }
        }
        return maxArea;

    }
}