代码随想录算法训练营第五十九天 | 下一个更大元素 II、接雨水

● 今日学习的文章链接和视频链接

题目503. 下一个更大元素 II
题目42. 接雨水

● 看到题目的第一想法

基本套路差不多 就是找第一个更大的

● 看完代码随想录之后的想法

接雨水还是尽量掌握双指针的更简单

● 实现过程中遇到哪些困难

接雨水

● 解题代码

1. 点击查看代码

   class Solution {
       public int[] nextGreaterElements(int[] nums) {
           if(nums.length == 1) return new int[]{-1};
           int len = nums.length;
           int size = nums.length;
           int[] result = new int[len];
           Stack<Integer> stack = new Stack<>();
           stack.push(0);
           Arrays.fill(result,-1);//默认全部初始化为-1
           for(int i = 1;i < 2 * nums.length;i++){
               if(nums[i % size] <= nums[stack.peek()]){
                   stack.push(i % size);
               }else if(!stack.isEmpty() && nums[i % size] > nums[stack.peek()]){
                   while(!stack.isEmpty() && nums[i % size] > nums[stack.peek()]){
                       result[stack.peek()] = nums[i % size];
                       stack.pop();
                   }
                   stack.push(i % size);
               }
           }
           return result;
       }
   }
   

2. 点击查看代码

   class Solution {
       public int trap(int[] height) {
           int size = height.length;
   
           if(size <= 2) return 0;
           Stack<Integer> stack = new Stack<Integer>();
           stack.push(0);
   
           int sum = 0;
           for(int index = 1;index < size;index++){
               int stackTop = stack.peek();
               if(height[index] < height[stackTop]){
                   stack.push(index);
               }else if(height[index] == height[stackTop]){
                   stack.pop();
                   stack.push(index);
               }else{
                   int heightAtIdx = height[index];
                   while (!stack.isEmpty() && (heightAtIdx > height[stackTop])){
                       int mid = stack.pop();
   
                       if (!stack.isEmpty()){
                           int left = stack.peek();
   
                           int h = Math.min(height[left], height[index]) - height[mid];
                           int w = index - left - 1;
                           int hold = h * w;
                           if (hold > 0) sum += hold;
                           stackTop = stack.peek();
                       }
                   }
                   stack.push(index);
               }
           }
           return sum;
       }
   }
   

● 今日收获，学习时长

今日收获：继续学习了单调栈
学习时长：1h