题目地址：HDU 1428
先用BFS+优先队列求出全部点到机房的最短距离。然后用记忆化搜索去搜。
代码例如以下：
#include <iostream>
#include <string.h>
#include <math.h>
#include <queue>
#include <algorithm>
#include <stdlib.h>
#include <map>
#include <set>
#include <stdio.h>
using namespace std;
#define LL __int64
#define pi acos(-1.0)
const int mod=1e9+7;
const int INF=0x3f3f3f3f;
const double eqs=1e-9;
const int MAXN=50+10;
int d[MAXN][MAXN], mp[MAXN][MAXN], vis[MAXN][MAXN], n;
LL dp[MAXN][MAXN];
int jx[]={0,0,1,-1};
int jy[]={1,-1,0,0};
struct node
{
int x, y, step;
bool operator < (const node &tmp) const{
return tmp.step<step;
}
};
void bfs()
{
node f1, f2;
f1.x=n-1;
f1.y=n-1;
f1.step=mp[n-1][n-1];
d[n-1][n-1]=mp[n-1][n-1];
vis[n-1][n-1]=1;
priority_queue<node>q;
q.push(f1);
while(!q.empty()){
f1=q.top();
q.pop();
for(int i=0;i<4;i++){
f2.x=f1.x+jx[i];
f2.y=f1.y+jy[i];
if(f2.x>=0&&f2.x<n&&f2.y>=0&&f2.y<n&&!vis[f2.x][f2.y]){
vis[f2.x][f2.y]=1;
f2.step=f1.step+mp[f2.x][f2.y];
d[f2.x][f2.y]=f2.step;
q.push(f2);
}
}
}
}
LL dfs(int x, int y)
{
int i, a, b;
if(dp[x][y]) return dp[x][y];
for(i=0;i<4;i++){
a=x+jx[i];
b=y+jy[i];
if(a>=0&&a<n&&b>=0&&b<n&&d[a][b]<d[x][y]){
dp[x][y]+=dfs(a,b);
}
}
return dp[x][y];
}
int main()
{
int i, j;
while(scanf("%d",&n)!=EOF){
for(i=0;i<n;i++){
for(j=0;j<n;j++){
scanf("%d",&mp[i][j]);
}
}
memset(dp,0,sizeof(dp));
memset(vis,0,sizeof(vis));
bfs();
dp[n-1][n-1]=1;
printf("%I64d
",dfs(0,0));
}
return 0;
}