58 lines
1.4 KiB
C++
58 lines
1.4 KiB
C++
#include <iostream>
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#include <cstdlib>
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#include <cstdio>
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#include <queue>
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#include <cstring>
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#include <algorithm>
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#define RD(x) scanf("%d",&x)
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#define RD2(x,y) scanf("%d%d",&x,&y)
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#define RD3(x,y,z) scanf("%d%d%d",&x,&y,&z)
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#define clr0(x) memset(x,0,sizeof(x))
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#define clr1(x) memset(x,-1,sizeof(x))
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using namespace std;
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typedef long long LL;
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const int maxn = 1005;
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const double eps = 1e-3;
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const int inf = 0x7fffffff;
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char p[maxn];
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const LL mod = 1000000007;
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LL c[maxn][maxn];
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LL q[maxn];
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void init()
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{
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for(int i = 0 ; i < maxn ; ++i){
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c[i][0] = 1;
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}
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for(int i = 1 ; i < maxn ; i++){
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for(int j = 1 ; j <= i ; ++j){
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c[i][j] = (c[i-1][j-1] + c[i-1][j])%mod;
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}
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}
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q[0] = 1;
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for(int i = 1;i < maxn;++i){
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q[i] = (q[i - 1]*2)%mod;
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}
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}
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int main()
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{
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init();
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int n,k;
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while(~scanf("%d%s",&n,p)){
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int m = strlen(p);
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int k = 0;
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LL ans = 0,tmp = 0;
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for(int st = 0;st < m;++st){
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if(p[st] == '1'){
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ans += ((m-st-2>=0&&n-k-1>=0?c[m - st - 2][n - k - 1]:0) * (q[m - st - 1] - 1))%mod;
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ans += (tmp * q[m - st]%mod * (m-st-1>=0&&n-k>=0?c[m - st - 1][n - k]:0))%mod;
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ans %= mod;
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}
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tmp = (tmp*2 + p[st] - '0')%mod;
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k += p[st] - '0';
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}
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if(ans < 0) ans += mod;
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printf("%I64d\n",ans);
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}
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return 0;
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}
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