Smallest Difference(POJ-2718)

暴搜一下就行了，确实也没法优化什么。 不过枚举一半，另一半用next_permutation()函数应该是会快一些的。

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<queue>
#include<cmath>
using namespace std;
int T,a[20],n,vis[20],tot;
int A[20],B;
void dfs(int cur) {
    if(cur==n/2) {
        int b[20],kase = 0;
        for(int i=0;i<n;i++) {
            if(!vis[i]) b[kase++] = a[i];
        }
        sort(b,b+kase);
        do {
            int t=0;
            if(b[0]==0&&n-cur>1) continue;
            for(int i=0;i<kase;i++)
                t = t*10 + b[i];
            int c = abs(t-B);
            if(c<tot) tot = c;
        } while(next_permutation(b,b+kase));
    }
    else for(int i=0;i<n;i++) {
        if(cur==0&&a[i]==0) continue;
        if(!vis[i]) {
            B=B*10+a[i];
            A[cur] = a[i];
            vis[i] = 1;
            dfs(cur+1);
            B = (B-a[i])/10;
            vis[i] = 0;
        }
    }
}
int main() {
    scanf("%d",&T);
    char c = getchar();
    while(T--) {
        char s[100];
        int kase = 0;
        gets(s);
        n = strlen(s);
        for(int i=0;i<n;i++) {
            if(s[i]!=' ') {
                a[kase++] = s[i]-'0';
            }
        }
        n = kase;
        memset(vis,0,sizeof(vis));
        memset(A,0,sizeof(A));
        B = 0;
        tot = 1000000000;
        dfs(0);
        printf("%d\n",tot);
    }
    return 0;
}