Necklace (全排列 + 匈牙利)

#include<bits/stdc++.h>
using namespace std;

bool noway[][], Gra[][];
int arr[];

int linker[];
bool used[];
bool dfs(int u, int vN) {
    for(int v = ; v <= vN; v++)
        if(Gra[u][v] && !used[v]) {
            used[v] = true;
            if(linker[v] == - || dfs(linker[v], vN)) {
                linker[v] = u;
                return true;
            }
        }
    return false;
}
int hungary(int vN) {
    int res = ;
    memset(linker,-,sizeof(linker));
    for(int u = ; u <= vN; u++) {
        memset(used,false,sizeof(used));
        if(dfs(u, vN))
            res++;
    }
    return vN - res;
}

int solve(int n) {
    memset(Gra, true, sizeof(Gra));
    for(int i = ; i <= n; i ++)
        for(int j = ; j <= n; j ++)
            if(noway[arr[i - ]][j] || noway[arr[i]][j])
                Gra[i][j] = false;
    for(int i = ; i <= n; i ++)
        if(noway[arr[]][i] || noway[arr[n]][i])
            Gra[][i] = false;
    return hungary(n);
}

int main() {
    int n,m,a,b;
    while(~scanf("%d%d",&n,&m)) {
        if(n == ){
            printf("0\n");
            continue;
        }
        memset(noway, false, sizeof(noway));
        for(int i = ; i < m; i ++) {
            scanf("%d%d",&a,&b);
            noway[b][a] = true;
        }
        int ans = ;
        for(int i = ; i <= n; i ++) arr[i] = i;
        do {
            ans = min(solve(n), ans);
        } while(next_permutation(arr + , arr + n + ));
        printf("%d\n",ans);
    }
    return ;
}