usaco 1.5 numtri...超时的搜索...

/*
    ID:chenjiong
    PROG:numtri
    LANG:C++
*/

#include <stdio.h>
#include <string.h>

const int MAXN = 1005;

int N;
int mat[MAXN][MAXN];
int cnt;
int sum;
int max = 0;

void dfs(int x,int y)
{
    if ( x == N )
    {
        if ( sum > max )
            max = sum;
        return;
    }

    sum += mat[x + 1][y];
    dfs(x + 1,y);
    sum -= mat[x + 1][y];
        
    sum += mat[x + 1][y + 1];
    dfs(x + 1,y + 1);
    sum -= mat[x + 1][y + 1];

}

int main()
{
    freopen("numtri.in","r",stdin);
    freopen("numtri.out","w",stdout);

    int i,j;
    scanf("%d",&N);
    for ( i = 0; i < N; i++)
        for ( j = 0; j <= i; j++)
            scanf("%d",&mat[i][j]);

    sum = mat[0][0];
    dfs(0,0);

    printf("%d\n",max);
    return 0;
}