# [Leetcode]739. Daily Temperatures

Given a list of daily temperatures T, return a list such that, for each day in the input, tells you how many days you would have to wait until a warmer temperature. If there is no future day for which this is possible, put 0 instead.
For example, given the list of temperatures T = [73, 74, 75, 71, 69, 72, 76, 73], your output should be [1, 1, 4, 2, 1, 1, 0, 0].
Note: The length of temperatures will be in the range [1, 30000]. Each temperature will be an integer in the range [30, 100].

This is a great exercise for Monotonic Stack. Monotonic stack is a stack when the items in it are kept in order (monotonically increasing or monotonically decreasing). One of the properties of it is that:

• With a monotonically increasing stack, you can find the first item that is smaller than each item.
• With a monotonically decreasing stack, you can find the first item that is larger than each item.

#### Logic

We use monotonically decreasing stack mono. Iterating from the left to the right:

• when we meet an element that is smaller than the top element in mono, we would push it to mono.
• when we meet an element that is larger than the top element in mono, we pop it.

#### Code

class Solution:
def dailyTemperatures(self, T: List[int]) -> List[int]:
mono,n = [],len(T)
ret = [0] * n
for i,val in enumerate(T):
while mono and val > mono[-1][1]:
pre_i,pre_v = mono.pop()
ret[pre_i] = i - pre_i
mono.append((i,val))
return ret


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