Daily Temperatures | LeetCode | Stack Solution Explained
739. Daily Temperatures LeetCode becomes easier to solve with the knowledge of Next Greatest Element (NGE). I explain the approach & the implementation. Problem Link.
0. Daily Temperatures: Problem Discussion
- Given: List of integer values of temperatures
- Goal: Return a list of integer values that are days (indices) until a warmer day arrives
temperatures = [30,40,40,60] return [1,2,1,0]
1. Daily Temperatures: Observations & Logic
My first instinct was to think about the Next Greatest Element approach. I explain how I reached the intuitions here:
Post Link: Next Greater Element I | Solution Explained + Stack Optimization
Once you understand the intuition for the Next Greatest Element, the rest is just implementation.
2. Daily Temperatures: Implementation
class Solution: def dailyTemperatures(self, temps: List[int]) -> List[int]: stack =  ans = *len(temps) for index, item in enumerate(temps): while stack and item > stack[-1]: it, ind = stack.pop() ans[ind] = index-ind stack.append((item, index)) return ans
2.1. Complexity Analysis
- Time: O(N). It may look like we are going backwards by popping elements rather arbitarily and for arbitary amounts of time. However, from the perspective of a single element, it sees only two operations – insertion into the stack & removal from the stack. That’s all. This means there are 2 operations for each element or, 2N total operations.
- Space: O(N) to store the stack.
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