739. Daily Temperatures - LeetCode

Question

739. Daily Temperatures

Solution

題目大意：比今天溫度還要高還須要幾天

思路：笨方法實現，每次遍歷將來幾天，比今天溫度高，就座標減

Java實現：

public int[] dailyTemperatures(int[] temperatures) {
    int[] ans = new int[temperatures.length];
    for (int i = 0; i<temperatures.length; i++) {
        int highIdx = i;
        for (int j=i+1; j<temperatures.length; j++) {
            if (temperatures[j] > temperatures[i]) {
                highIdx = j;
                break;
            }
        }
        ans[i] = highIdx - i;
    }
    return ans;
}

Ref

別人實現高效的方法

https://leetcode.com/problems/daily-temperatures/discuss/109832/Java-Easy-AC-Solution-with-Stack

Stack

public int[] dailyTemperatures(int[] temperatures) {
    Stack<Integer> 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;
}

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;
}