ICPCCamp 2016 Day 6 - Spb SU and Spb AU Contest(Set intersection-随机)

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题意：给n＋1个01串，每个串长度为2n，从中找出2个01串，它们前2n位里同一位上出现相同0，1的次数≥n/2
保证有解，输出任意解。

随机试即可，求证明

#include <iostream>#include <cmath>#include <algorithm>#include <cstdio>#include <cstring>#include <string>#include <vector>#include <map>#include <functional>#include <cstdlib>#include <queue>#include <stack>using namespace std;#define For(i,n) for(int i=1;i<=n;i++)#define Fork(i,k,n) for(int i=k;i<=n;i++)#define Rep(i,n) for(int i=0;i<n;i++)#define ForD(i,n) for(int i=n;i;i--)#define ForkD(i,k,n) for(int i=n;i>=k;i--)#define RepD(i,n) for(int i=n;i>=0;i--)#define Forp(x) for(int p=Pre[x];p;p=Next[p])#define Forpiter(x) for(int &p=iter[x];p;p=Next[p])  #define Lson (o<<1)#define Rson ((o<<1)+1)#define MEM(a) memset(a,0,sizeof(a));#define MEMI(a) memset(a,127,sizeof(a));#define MEMi(a) memset(a,128,sizeof(a));#define INF (500000000000LL)#define F (100000007)#define pb push_back#define mp make_pair #define fi first#define se second#define vi vector<int> #define pi pair<int,int>#define SI(a) ((a).size())typedef long long ll;typedef unsigned long long ull;ll mul(ll a,ll b){return (a*b)%F;}ll add(ll a,ll b){return (a+b)%F;}ll sub(ll a,ll b){return (a-b+llabs(a-b)/F*F+F)%F;}void upd(ll &a,ll b){a=(a%F+b%F)%F;}int read(){    int x=0,f=1; char ch=getchar();    while(!isdigit(ch)) {if (ch=='-') f=-1; ch=getchar();}    while(isdigit(ch)) { x=x*10+ch-'0'; ch=getchar();}    return x*f;} #define MAXN (6000+10)int n,m;int a[MAXN][1000];char s[MAXN];int check(int i,int j) {    int ans=0;    Rep(k,m)         ans+=__builtin_popcount(a[i][k]&a[j][k]);    return ans;}int main() {    n=read();    For(i,n+1) {        scanf("%s",s);        m=strlen(s);        Rep(j,m)            a[i][j]=s[j]-33;    }    srand(time(NULL));    while(1) {        int i=rand()%(n+1)+1;        int j=rand()%(n+1)+1;        if (i!=j && check(i,j)>=n/2) {            if (i<j) swap(i,j);            cout<<i << ' '<<j<<endl;            return 0;        }    }    return 0;}

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