HDU 4620 Fruit Ninja Extreme 搜索

搜索+最优性剪枝。

DFS的下一层起点应为当前选择的 i 的下一个，即DFS(i + 1)而不是DFS( cur + 1 )，cur+1代表当前起点的下一个。没想清楚，TLE到死……

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <algorithm>

using namespace std;

const int MAXN = 40;

struct node
{
    int t, id;
    int cnt;
    int fruit[12];
};

int N, M, W;
int ansN, tmpN;
node D[MAXN];
int tmp[MAXN];
int ans[MAXN];
bool vis[320];

bool cmp( node a, node b )
{
    return a.t < b.t;
}

void chuli( int cnt )
{
    for ( int i = 0; i < cnt; ++i )
        ans[i] = tmp[i];
    return;
}

int change( int i, int *temp )
{
    int cnt = 0;
    for ( int j = 0; j < D[i].cnt; ++j )
    {
        int idx = D[i].fruit[j];
        if ( !vis[ idx ] )
            temp[cnt] = idx, ++cnt;
    }
    return cnt;
}

void MyRestore( int *temp, int cnt )
{
    
    for ( int j = 0; j < cnt; ++j )
    {
        vis[ temp[j] ] = false;
    }
    return;
}

void DFS( int cur, int pre, int sum )
{
    if ( tmpN > ansN )
    {
        ansN = tmpN;
        chuli( tmpN );
    }
    if ( cur >= N ) return;
    if ( tmpN + N - cur <= ansN ) return;
    if ( M - sum < 3 ) return;

    for ( int i = cur; i < N; ++i )
    {
        if ( pre != -1 && D[i].t - D[pre].t > W ) break;

        if ( D[i].cnt < 3 ) continue;
        int temp[20];
        int left = change( i, temp );
        if ( left < 3 ) continue;

        for ( int j = 0; j < left; ++j )
        {
            int idx = temp[j];
            vis[idx] = true;
        }

        tmp[ tmpN++ ] = D[i].id;
        DFS( i + 1, i, sum + left );  //i+1 不是 cur+1 !!!!!
        --tmpN;
        MyRestore( temp, left );
    }

    return;
}

int main()
{
    //freopen( "1010.in", "r", stdin );
    //freopen( "s.out", "w", stdout );
    int T;
    scanf( "%d", &T );
    while ( T-- )
    {
        scanf( "%d%d%d", &N, &M, &W );
        for ( int i = 0; i < N; ++i )
        {
            D[i].id = i + 1;
            scanf("%d%d", &D[i].cnt, &D[i].t );
            for ( int j = 0; j < D[i].cnt; ++j )
                scanf( "%d", &D[i].fruit[j] );
        }
        sort( D, D + N, cmp );

        ansN = 0;
        tmpN = 0;
        memset( vis, false, sizeof(vis) );
        DFS( 0, -1, 0 );

        sort( ans, ans + ansN );
        printf( "%d
", ansN );
        for ( int i = 0; i < ansN; ++i )
        {
            if ( i ) putchar(' ');
            printf( "%d", ans[i] );
        }
        puts("");
    }
    return 0;
}