hdu 1428 bfs+记忆化搜索

#include <iostream>
#include <queue>
using namespace std;

int map[55][55], n;
int dist[55][55];
__int64 dp[55][55];
const int INF = INT_MAX;
int dir[4][2] = {{1,0},{-1,0},{0,-1},{0,1}};
struct Node
{
    int x, y;
};
queue <Node> q;

void bfs()
{
    while (!q.empty())
    {
        q.pop();
    }
    Node first, next;
    first.x = n, first.y = n;
    dist[n][n] = map[n][n];
    q.push(first);
    while (!q.empty())
    {
        first = q.front();
        q.pop();
        int i;
        for (i = 0; i < 4; ++i)
        {
            next.x = first.x + dir[i][0];
            next.y = first.y + dir[i][1];
            if (next.x > 0 && next.x <= n && next.y > 0 && next.y <= n)
            {
                if (map[next.x][next.y] + dist[first.x][first.y] < dist[next.x][next.y])
                {
                    dist[next.x][next.y] = map[next.x][next.y] + dist[first.x][first.y];
                    q.push(next);
                }       
            }
        }
    }
}

__int64 Search(int x, int y)
{
    if (dp[x][y] != -1)
    {
        return dp[x][y];
    }
    else if (x == n && y == n)
    {
        return 1;
    }
    else
    {
        int i, fx, fy;
        __int64 sum = 0;
        for (i = 0; i < 4; ++i)
        {
            fx = x + dir[i][0];
            fy = y + dir[i][1];
            if (fx > 0 && fx <= n && fy > 0 && fy <= n && dist[fx][fy] < dist[x][y])
            {
                sum += Search(fx, fy);
            }
        }
        dp[x][y] = sum;
        return sum;
    }
}

int main()
{
    while (scanf("%d", &n) != EOF && n)
    {
        int i, j;
        for (i = 1; i <= n; ++i)
        {
            for (j = 1; j <= n; ++j)
            {
                dist[i][j] = INF;
                scanf("%d", &map[i][j]);
            }
        }
        bfs();
        memset(dp, -1, sizeof(dp));
        Search(1,1);
        printf("%I64d\n", dp[1][1]);
    }
    return 0;
}