# 681.Next-Closest-Time

## 题目描述

Given a time represented in the format "HH:MM", form the next closest time by reusing the current digits. There is no limit on how many times a digit can be reused.
You may assume the given input string is always valid. For example, "01:34", "12:09" are all valid. "1:34", "12:9" are all invalid.
Example 1:
Input: "19:34"
Output: "19:39"
Explanation: The next closest time choosing from digits 1, 9, 3, 4, is 19:39, which occurs 5 minutes later. It is not 19:33, because this occurs 23 hours and 59 minutes later.
Example 2:
Input: "23:59"
Output: "22:22"
Explanation: The next closest time choosing from digits 2, 3, 5, 9, is 22:22. It may be assumed that the returned time is next day's time since it is smaller than the input time numerically.

## 代码

### Approach #1

Time Complexity: O(1). We try up to 24 * 60 possible times until we find the correct time
Space Complexity: O(1)
class Solution {
public String nextClosestTime(String time) {
int cur = 60 * Integer.parseInt(time.substring(0, 2));
cur += Integer.parseInt(time.substring(3));
Set<Integer> allowed = new HashSet();
for (char c: time.toCharArray()) {
if (c != ':') {
}
}
while (true) {
cur = (cur + 1) % (24 * 60);
int[] digits = new int[] {cur / 60 / 10, cur / 60 % 10,
cur % 60 / 10, cur % 60 % 10};
search : {
for (int d: digits) {
if (!allowed.contains(d))
break search;
}
return String.format("%02d:%02d", cur / 60, cur % 60);
}
}
}
}

### Approach #2 Build From Allowed Digits

class Solution {
public String nextClosestTime(String time) {
int start = 60 * Integer.parseInt(time.substring(0, 2));
start += Integer.parseInt(time.substring(3));
int ans = start;
int elapsed = 24 * 60;
Set<Integer> allowed = new HashSet();
for (char c: time.toCharArray()) {
if (c != ':') {
}
}
for (int h1: allowed) {
for (int h2: allowed) {
if (h1 * 10 + h2 < 24) {
for (int m1: allowed) {
for (int m2: allowed) {
if (m1 * 10 + m2 < 60) {
int cur = 60 * (h1 * 10 + h2) + (m1 * 10 + m2);
int candElapsed = Math.floorMod(cur - start, 24 * 60);
if (0 < candElapsed && candElapsed < elapsed) {
ans = cur;
elapsed = candElapsed;
}
}
}
}
}
}
}
return String.format("%02d:%02d", ans / 60, ans % 60);
}
}