wenbao与随机

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https://loj.ac/problem/526

比赛的时候各种知识搞都没有ac，题解说利用二分图，看到大佬用random过，佩服！

#include <iostream>
#include <algorithm>
#include <ctime>
#include <vector>
using namespace std;

#define ll long long
ll a[555], b[555];

ll g(ll x, ll y){
    return !y ? x : g(y, x%y);
}

bool ok(ll x, ll y){
    if(g(x, y) == 1 && g(x+1LL, y+1LL) == 1) return false;
    return true;
}

int main(){
    int n, num1 = 0, num2 = 0;
    scanf("%d", &n);
    for(int i = 0; i < n; ++i){
        scanf("%lld", &a[i]);
        if(a[i]&1) num1++;
        else num2 ++;
    }
    int ma = max(num1, num2);
    while(clock() < 0.9*CLOCKS_PER_SEC){
        random_shuffle(a, a+n);
        for(int k = 0; k < 2; ++k){
            int num = 0;
            for(int i = 0; i < n; ++i){
                bool flag = true;
                for(int j = 0; j < num; ++j){
                    if(!ok(a[i], b[j])){
                        flag = false;
                        break;    
                    }
                }
                if(flag) b[num++] = a[i];
            }
            ma = max(ma, num);
        }
    }
    printf("%d
", ma);
    return 0;
}

CLOCKS_PER_SEC表示每秒钟包含的系统时间单位数

延时循环

void waiting(void) {  
    cout<<"Enter the delay time, in seconds: ";  
    float secs;  
    cin>>secs;  
    clock_t delay=secs * CLOCKS_PER_SEC; //convert to clock ticks  
    cout<<"startinga
";  
    clock_t start=clock();  
    while (clock()-start < delay)//wait until time elapses  
        ;//note the semicolon  
    cout<<"done a
";  
    cin.get();  
}  

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http://codeforces.com/contest/862/problem/C

n个数（不超过1e6）的异或为x

#include <iostream>
#include <algorithm>
using namespace std;
const int maxn = 1e6;
int a[maxn], n, x;
bool ok(){
    random_shuffle(a, a+maxn);
    int tmp = x;
    for(int i = 0; i < n-1; ++i){
        tmp ^= a[i];
    }
    a[n-1] = tmp;
    for(int i = 0; i < n-1; ++i){
        if(tmp == a[i]) return false;
    }
    return true;
}
int main(){
    scanf("%d%d", &n, &x);
    if(n == 1) {
        printf("YES
%d
", x);
    }else if(n == 2){
        if(x == 0) printf("NO
");
        else printf("YES
0 %d
", x);
    }else{
        for(int i = 0; i < maxn; ++i){
            a[i] = i;
        }
        printf("YES
");
        while(!ok());
        for(int i = 0; i < n; ++i){
            printf("%d%c", a[i], " 
"[i == n-1]);
        }
    }
    return 0;
}

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只有不断学习才能进步！