Next Closest Time

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.

思路：try all possiblity；diff <= 0 ， + 24 hours

class Solution {
    public String nextClosestTime(String time) {
        if(time == null || time.length() == 0) {
            return time;
        }    
        HashSet<Character> visited = new HashSet<>();
        StringBuilder sb = new StringBuilder();
        for(int i = 0; i < time.length(); i++) {
            char c = time.charAt(i);
            if(!visited.contains(c) && c != ':') {
                sb.append(c);
            }
        }
        
        String[] small = {""};
        dfs(time, sb.toString(), small, "");
        return small[0];
    }
    
    private int smallDiff = Integer.MAX_VALUE;
    
    private void dfs(String time, String source, String[] small, String curstr) {
        if(curstr.length() == 4) {
            if(isvalid(curstr)) {
                String candidate = curstr.substring(0, 2) + ":" + curstr.substring(2);
                int diff = convertStringToTime(candidate) - convertStringToTime(time);
                if(diff <= 0) {
                    diff += 24 * 60;
                }
                if(diff < smallDiff) {
                    smallDiff = diff;
                    small[0] = candidate;
                }
            }
            return;
        }
        for(int i = 0; i < source.length(); i++) {
            char c = source.charAt(i);
            dfs(time, source, small, curstr + c);
        }
    }
    
    private boolean isvalid(String curstr) {
        String hour = curstr.substring(0, 2);
        String min = curstr.substring(2);
        return 0 <= Integer.parseInt(hour) && Integer.parseInt(hour) <= 24 
            && 0 <= Integer.parseInt(min) && Integer.parseInt(min) <= 59;
    }
    
    private int convertStringToTime(String str) {
        String[] splits = str.split(":");
        String hour = splits[0];
        String min = splits[1];
        return Integer.parseInt(hour) * 60  + Integer.parseInt(min);
    }
}