Backtracking-401. Binary Watch

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".

class Solution {
public:
    void DFS(int len, int k, int curIndex, int val, vector<int>& vec)
    {
        if(k== && len== && val < ) vec.push_back(val);
        if(k== && len== && val < ) vec.push_back(val);
        if(curIndex == len || k == ) return;
        DFS(len, k, curIndex+, val, vec);
        val += pow(, curIndex), k--, curIndex++;
        DFS(len, k, curIndex, val, vec);
    }  

    vector<string> readBinaryWatch(int num) {
        vector<string> ans;
        for(int i = max(, num-); i <= min(, num); i++)
        {
            vector<int> vec1, vec2;
            DFS(, i, , , vec1), DFS(, num-i, , , vec2);
            for(auto val1: vec1)
                for(auto val2: vec2)
                {
                    string str = (to_string(val2).size()==?"":"") + to_string(val2);
                    ans.push_back(to_string(val1)+":"+ str);
                }
        }
        return ans;
    }
};