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739. Daily Temperatures 👍

  • Time: $O(n)$
  • Space: $O(n)$
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class Solution {
 public:
  vector<int> dailyTemperatures(vector<int>& temperatures) {
    vector<int> ans(temperatures.size());
    stack<int> stack;  // a decreasing stack

    for (int i = 0; i < temperatures.size(); ++i) {
      while (!stack.empty() && temperatures[stack.top()] < temperatures[i]) {
        const int index = stack.top();
        stack.pop();
        ans[index] = i - index;
      }
      stack.push(i);
    }

    return ans;
  }
};

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class Solution {
  public int[] dailyTemperatures(int[] temperatures) {
    int[] ans = new int[temperatures.length];
    Deque<Integer> stack = new ArrayDeque<>(); // a decreasing stack

    for (int i = 0; i < temperatures.length; ++i) {
      while (!stack.isEmpty() && temperatures[stack.peek()] < temperatures[i]) {
        final int index = stack.pop();
        ans[index] = i - index;
      }
      stack.push(i);
    }

    return ans;
  }
}

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class Solution:
  def dailyTemperatures(self, temperatures: list[int]) -> list[int]:
    ans = [0] * len(temperatures)
    stack = []  # a decreasing stack

    for i, temperature in enumerate(temperatures):
      while stack and temperature > temperatures[stack[-1]]:
        index = stack.pop()
        ans[index] = i - index
      stack.append(i)

    return ans