401. Binary Watch 2019-03-26

1.回溯题。递归实现.

class Solution {

    //public static List list=new ArrayList();

    public List readBinaryWatch(int num) {

        List list=new ArrayList();

        int[] a=new int[4];

int[] b=new int[6];

Arrays.fill(a,0);

Arrays.fill(b,0);

backTracking(list,0,0,num,a,b);

return list;

}

public static void backTracking(List list,int hour,int minute,int num,int[] a,int[] b) {

int[] a2=new int[4];

int[] b2=new int[6];

for(int i=0;i

a2[i]=a[i];

}

for(int i=0;i

b2[i]=b[i];

}

if(num==0) {

String s1=String.valueOf(hour);

String s2=String .valueOf(minute);

if(minute<10) {

s2="0"+s2;

}

list.add(s1+":"+s2);

}else {

            for(int i=0;i

if(b2[i]==0) {

if(minute+Math.pow(2, i)<=59) {

b2[i]=1;

backTracking(list,hour,minute+(int)(Math.pow(2, i)),num-1,a2,b2);

}

}

}

for(int i=0;i

if(a2[i]==0) {

if(Math.pow(2, i)+hour<=11) {

a2[i]=1;

backTracking(list,hour+(int)(Math.pow(2, i)),minute,num-1,a2,b2);

}

}

}

}

}

}