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].

给一个每天温度的数组，对于每一天，找出下一个比当前温度大的元素，记录它们之间的天数。

解法：栈，递减栈Descending Stack，新建一个长度和T相等的数组res，来记录天数。遍历数组，如果栈为空，直接如栈。如果栈不为空，且当前数字大于栈顶元素，pop出栈顶元素，求出下标差，也就是升温的天数，把这个差值记录给栈顶元素在res中的位置。然后继续看新的栈顶元素，直到当前数字小于等于栈顶元素停止。然后将当前数字入栈。最后返回res。

Java: Stack

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

Java: Array

public int[] dailyTemperatures(int[] temperatures) {    int[] stack = new int[temperatures.length];    int top = -1;    int[] ret = new int[temperatures.length];    for(int i = 0; i < temperatures.length; i++) {        while(top > -1 && temperatures[i] > temperatures[stack[top]]) {            int idx = stack[top--];            ret[idx] = i - idx;        }        stack[++top] = i;    }    return ret;}　

Python:

# Time:  O(n)# Space: O(n)class Solution(object):    def dailyTemperatures(self, temperatures):        """        :type temperatures: List[int]        :rtype: List[int]        """        result = [0] * len(temperatures)        stk = []        for i in xrange(len(temperatures)):            while stk and \                  temperatures[stk[-1]] < temperatures[i]:                idx = stk.pop()                result[idx] = i-idx            stk.append(i)        return result　　

Python: wo

class Solution(object):    def dailyTemperatures(self, T):        """        :type T: List[int]        :rtype: List[int]        """        st = []        res = [0] * len(T)        for i in xrange(len(T)):            if not st or T[i] <= T[st[-1]]:                st.append(i)            else:                while st and T[i] > T[st[-1]]:                     j = st.pop()                    res[j] = i - j                st.append(i)                                                   return res

C++:

// Time:  O(n)// Space: O(n)class Solution {public:    vector
     
       dailyTemperatures(vector
      
       & temperatures) {        vector
       
         result(temperatures.size());        stack
        
          stk;        for (int i = 0; i < temperatures.size(); ++i) {            while (!stk.empty() &&                   temperatures[stk.top()] < temperatures[i]) {                const auto idx = stk.top(); stk.pop();                result[idx] = i - idx;            }            stk.emplace(i);        }        return result;     }};
        
       
      
     

　　　　

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