[LeetCode] 539. Minimum Time Difference

Given a list of 24-hour clock time points in "Hour:Minutes" format, find the minimum minutes difference between any two time points in the list.

Example 1:

Input: ["23:59","00:00"]
Output: 1

Note:

1. The number of time points in the given list is at least 2 and won't exceed 20000.
2. The input time is legal and ranges from 00:00 to 23:59.

最小时间差。题意是给一些以字符串list表示的时间，请你找出这中间最小的时间差。例子给的不是很好，因为list不止两个元素。

这道题不涉及算法，不过最优解比较考验你对时间的敏感度。首先，既然时间是在00:00 - 23:59这个范围内被表示出来，所以最坏也就是1440种情况，所以可以创建一个长度为1440的布尔数组记录哪些时间出现过。之后遍历这个布尔数组，看看哪两个时间之间的时间差最小。注意记得去“模”24小时。

时间O(n)

空间O(n)

Java实现

class Solution {
    public int findMinDifference(List<String> timePoints) {
        boolean[] mark = new boolean[24 * 60];
        for (String time : timePoints) {
            String[] t = time.split(":");
            int h = Integer.parseInt(t[0]);
            int m = Integer.parseInt(t[1]);
            if (mark[h * 60 + m]) {
                return 0;
            }
            mark[h * 60 + m] = true;
        }

        int prev = 0;
        int min = Integer.MAX_VALUE;
        int first = Integer.MAX_VALUE;
        int last = Integer.MIN_VALUE;
        for (int i = 0; i < 24 * 60; i++) {
            if (mark[i]) {
                if (first != Integer.MAX_VALUE) {
                    min = Math.min(min, i - prev);
                }
                first = Math.min(first, i);
                last = Math.max(last, i);
                prev = i;
            }
        }
        min = Math.min(min, (24 * 60 - last + first));
        return min;
    }
}

LeetCode 题目总结