Stack: daily temperature

subject

https://leetcode-cn.com/problems/iIQa4I/

Their thinking

Save the subscript of daily temperature in the array with a stack , And maintain a monotonically decreasing stack .

step ：

1. Push ： Traverse daily temperature , If the stack is empty , Save the current temperature to the stack .（ Save subscript ）.
2. Out of the stack ： Compare the top element with the current temperature , If the stack top element is less than the current temperature , Out of the stack , Complete the statistics of the last heating days . Continue to stack to determine whether there are days less than the current temperature , Finally, subscript the array of current temperature onto the stack .
3. state ： As long as the current temperature is greater than the elements in the stack , We'll be out of the stack , So we can find that the stack is always decreasing .

Why choose a data structure ： Stack .
Because we need to compare the current temperature with the previous temperature , So this is a derivation process from back to front , Consider choosing a stack as a data set .

Code

class Solution {
    
    public int[] dailyTemperatures(int[] temperatures) {
    
        Stack<Integer> stack = new Stack<>();
        int[] result = new int[temperatures.length];
        for(int i = 0; i < temperatures.length; i++) {
    
            while(!stack.isEmpty() && temperatures[stack.peek()] <  temperatures[i]) {
    
                  int preIndex = stack.pop();
                  result[preIndex] = i - preIndex;
            }
            stack.push(i);
        }
        return result;
    }
}

summary

Subscript the daily temperature in the array with a stack , Maintain a monotonic decreasing stack .