hdu 4016搜索

这题看完本来以为是找规律的，可找了半天也没找出啥规律，翻了一下解题报告，说是搜索加剪枝，学了一下，就过了。

/*
 * hdu4016/win.cpp
 * Created on: 2012-11-9
 * Author    : ben
 */
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <ctime>
#include <iostream>
#include <algorithm>
#include <queue>
#include <set>
#include <map>
#include <stack>
#include <string>
#include <vector>
#include <deque>
#include <list>
#include <functional>
#include <numeric>
#include <cctype>
using namespace std;
typedef long long LL;
const int MAXN = 42;
const LL MAX = 0x7fffffffffffffffLL;
int n, k;
LL data[MAXN], ans, ands[MAXN];

void dfs(int now, int step, LL num) {
    if(num < ans) {
        ans = num;
    }
    if(now == n || step == k) return ;
    if((num & ands[now]) < ans) {
        dfs(now + 1, step + 1, num & data[now]);
        dfs(now + 1, step, num);
    }
}

int main() {
#ifndef ONLINE_JUDGE
    freopen("data.in", "r", stdin);
#endif
    int T;
    scanf("%d", &T);
    for(int t = 1; t <= T; t++) {
        scanf("%d%d", &n, &k);
        for(int i = 0; i < n; i++) {
            scanf("%I64d", &data[i]);
        }
        sort(data, data + n);
        copy(data, data + n, ands);
        ands[n] = MAX;
        for(int i = n - 1; i >= 0; i--) {
            ands[i] &= ands[i + 1];
        }
        ans = data[0];
        dfs(0, 0, MAX);
        printf("Case #%d: %I64d\n", t, ans);
    }
    return 0;
}