LeetCode: Daily Temperatures

## https://code.dennyzhang.com/daily-temperatures
## Basic Ideas: Monotonous stack can help us find first largest element in O(n) time complexity.
##
##              Descending stack: find the next bigger nubmer for each element
##
##              For any given number, if we haven't met the bigger number. We push it to the stack
##              If we pop out one element, we do find a bigger number than this element.
##
## Complexity: Time O(n), Space O(n)
class Solution(object):
    def dailyTemperatures(self, temperatures):
        """
        :type temperatures: List[int]
        :rtype: List[int]
        """
        length = len(temperatures)
        res = [0]*length
        stack = []
        for i in xrange(length):
            # If current number is bigger, we solved the previous puzzles
            while len(stack) != 0 and temperatures[i] > temperatures[stack[-1]]:
                k = stack.pop()
                # t[i] is the next bigger number than t[k]
                res[k] = i-k
            stack.append(i)
        return res