A binary watch has 4 LEDs on the top which represent the hours (0-11), and the 6 LEDs on the bottom represent the minutes (0-59).
Each LED represents a zero or one, with the least significant bit on the right.
For example, the above binary watch reads "3:25".
Given a non-negative integer n which represents the number of LEDs that are currently on, return all possible times the watch could represent.
Example:
Input: n = 1 Return: ["1:00", "2:00", "4:00", "8:00", "0:01", "0:02", "0:04", "0:08", "0:16", "0:32"]
Note:
- The order of output does not matter.
- The hour must not contain a leading zero, for example "01:00" is not valid, it should be "1:00".
- The minute must be consist of two digits and may contain a leading zero, for example "10:2" is not valid, it should be "10:02".
题目链接：https://leetcode-cn.com/problems/binary-watch/
思路
总体思路还是回溯法。
只是对于数字代表的含义需要进行判定。
最后生成的值需要判断其是否符合时间的要求。
class Solution {
public:
vector<string> res;
vector<string> readBinaryWatch(int num) {
if(num<0 || num>8) return res;
if(num==0){
res.push_back("0:00");
}else{
getTime(num, 0, 0, 0);
}
return res;
}
void getTime(int num, int hour, int min, int idx){
if(num==0){
if(hour<=11 && min<=59){
string time = to_string(hour) + ":" + (min<10?"0":"") + to_string(min);
res.push_back(time);
}
return;
}
for(int i=idx; i<=10-num; ++i){
int nhour = hour, nmin = min;
if(i/6){
nhour += pow(2, i%6);
}else{
nmin += pow(2, i);
}
getTime(num-1, nhour, nmin, i+1);
}
return;
}
};