題目鏈接:https://leetcode.com/problems/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".
思路:基本還是一道DFS的題目,分別在小時和分鐘上做DFS,給定幾個燈亮,然後把這些亮的燈枚舉分給小時和分鐘.需要注意的是剪枝,即小時必須小於12,分鐘小於60.然後將小時和分鐘組合即可.還有一個需要注意的是如果分鐘只有1位數,還要補0.
代碼如下:
class Solution {
public:
void DFS(int len, int k, int curIndex, int val, vector<int>& vec)
{
if(k==0 && len==4 && val < 12) vec.push_back(val);
if(k==0 && len==6 && val < 60) vec.push_back(val);
if(curIndex == len || k == 0) return;
DFS(len, k, curIndex+1, val, vec);
val += pow(2, curIndex), k--, curIndex++;
DFS(len, k, curIndex, val, vec);
}
vector<string> readBinaryWatch(int num) {
vector<string> ans;
for(int i = max(0, num-6); i <= min(4, num); i++)
{
vector<int> vec1, vec2;
DFS(4, i, 0, 0, vec1), DFS(6, num-i, 0, 0, vec2);
for(auto val1: vec1)
for(auto val2: vec2)
{
string str = (to_string(val2).size()==1?"0":"") + to_string(val2);
ans.push_back(to_string(val1)+":"+ str);
}
}
return ans;
}
};