0739-daily-temperatures

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Description

Given an array of integers temperatures represents the daily temperatures, return an array answer such that answer[i] is the number of days you have to wait after the ith day to get a warmer temperature. If there is no future day for which this is possible, keep answer[i] == 0 instead.

 

Example 1:

Input: temperatures = [73,74,75,71,69,72,76,73]
Output: [1,1,4,2,1,1,0,0]

Example 2:

Input: temperatures = [30,40,50,60]
Output: [1,1,1,0]

Example 3:

Input: temperatures = [30,60,90]
Output: [1,1,0]

 

Constraints:

• 1 <= temperatures.length <= 105
• 30 <= temperatures[i] <= 100

Solution(Python)

class Solution:
    def dailyTemperatures(self, temperatures: List[int]) -> List[int]:
        return self.monotonic_stack(temperatures)
    # bruteforce
    #   as we read through  each temperature
    #     i will count until something is greater
    # Time Complexity: O(n^2)
    # Space complexity: O(1)

    # montonic stack
    #  use stack to keep track of previous temperature with lower index
    #  once i found that my current temparture is greater then i will store the result
    #
    def monotonic_stack(self, temperatures: List[int]) -> List[int]:
        n = len(temperatures)
        # stack empty
        stack = []
        # result array with zero
        res = [0] * n
        # loop through 
        for i in range(n):
        #   compare the temp index in the stac k with current temperature if greater then update the result of stack
            while stack and temperatures[i] > temperatures[stack[-1]]:
                res[stack[-1]] = i - stack[-1]
        #    pop it 
                stack.pop()
        #   append my current index to stack
            stack.append(i)
        return res