401. Binary Watch -----M ！

A binary watch has 4 LEDs on the top to represent the hours (0-11), and 6 LEDs on the bottom to represent the minutes (0-59). Each LED represents a zero or one, with the least significant bit on the right.

• For example, the below binary watch reads "4:51".

Given an integer turnedOn which represents the number of LEDs that are currently on (ignoring the PM), return all possible times the watch could represent. You may return the answer in any order.

The hour must not contain a leading zero.

• For example, "01:00" is not valid. It should be "1:00".

The minute must consist of two digits and may contain a leading zero.

• For example, "10:2" is not valid. It should be "10:02".

 

Example 1:

Input: turnedOn = 1
Output: ["0:01","0:02","0:04","0:08","0:16","0:32","1:00","2:00","4:00","8:00"]

Example 2:

Input: turnedOn = 9
Output: []

 

Constraints:

• 0 <= turnedOn <= 10

A: 

就是实现题。   考的是细心。 值得再做

主要是实现各种permutation。

class Solution {

public:

vector<string> readBinaryWatch(int turnedOn) {

vector<string> res;

vector<int> M{32, 16, 8, 4, 2, 1};

for (int lenH = 0; lenH <= turnedOn; lenH++) {

if (lenH >= 4)

continue;

auto lenM = turnedOn - lenH;

if (lenM >= 6)

continue;

auto resH = getPermH(lenH);

auto resM = getPermM(M, 0, 0, lenM);

for (auto h : resH) {

for (auto m : resM) {

res.push_back(h + ":" + m);

}

}

}

return res;

}

private:

vector<string> getPermH(int len) {

vector<int> H{8, 4, 2, 1};

if (len == 0)

return {"0"};

if (len == 1) {

return {"1", "2", "4", "8"};

}

if (len == 2) {

return {"3", "5", "6", "10", "9"};

}

if (len == 3) {

return {"7", "11"};

}

return {};

}

vector<string> getPermM(vector<int>& M, int start, int preSum, int len) {

if(len<0 || start >= M.size())

return {};

if (len == 0) {

return {"00"};

}

vector<string> res;

if (len == 1) {

for (int i = start; i < M.size(); i++) {

if (M[i] + preSum < 60){

auto str = to_string(M[i] + preSum);

if(str.length() == 1)

str = "0"+str;

res.push_back(str);

}

}

return res;

}else{

res = getPermM(M, start + 1, preSum, len); // do not use this value

auto res2 = getPermM(M, start + 1, preSum + M[start], len - 1);

res.insert(res.end(), res2.begin(), res2.end());

}

return res;

}

};