spoj1182Sorted bit squence

Posted 2020-10-09 third2333

数位DP + 二分

 

 1 #include <iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 using namespace std;
 5 int n,m,k,f[33][33];
 6 void init()
 7 {
 8     f[0][0]=1;
 9     for(int i=1;i<=32;i++)
10     {
11         f[i][0]=f[i-1][0];
12         for(int j=1;j<=i;j++) f[i][j]=f[i-1][j-1]+f[i-1][j];
13     }
14 }
15 int cal(int x,int k)
16 {
17     int sum=0,tot=0,pos=0;
18     int bit[33];
19     memset(bit,0,sizeof(bit));
20     while(x)
21     {
22         bit[++pos]=x%2;
23         x/=2;
24     }
25     for(int i=pos;i>=1;i--)
26     {
27         if(!bit[i]) continue;
28         sum+=f[i-1][k-tot];
29         tot++;
30         if(tot>=k) break;
31     }
32     if(tot==k) sum++;
33     return sum;
34 }
35 int fnd(int l,int r,int k)
36 {
37     int i,num;
38     for(i=1;i<=31;i++)
39     {
40         num=cal(r,i)-cal(l-1,i);
41         if(num>=k) break;
42         else k-=num;
43     }
44     int tmp=l;
45     while(l<=r)
46     {
47         int mid=l+(r-l)/2;
48         num=cal(mid,i)-cal(tmp-1,i);
49         if(num>=k) r=mid-1;
50         else l=mid+1;
51     }
52     return l;
53 }
54 int main()
55 {
56    // freopen("cin.txt","r",stdin);
57     int t;
58     init();
59     scanf("%d",&t);
60     while(t--)
61     {
62         scanf("%d%d%d",&m,&n,&k);
63         if(m<0)
64         {
65             m&=~(1<<31);
66             if(n==0)
67             {
68                 n--;
69                 k--;
70             }
71             n&=~(1<<31);
72            // printf("m=%d n=%d\n",m,n);
73             printf("%d\n",(1<<31)|fnd(m,n,k));
74         }
75         else
76         {
77             if(m==0) k--,m++;
78             printf("%d\n",fnd(m,n,k));
79         }
80     }
81     return 0;
82 }