I know I can calculate the anwser directly,but I used DFS algorithm at first.I think it can solve this problem too,but I got WA on test #10,who can tell me WHY? thx.

My code:

/* ural1164 */

#include<iostream>
#include<string.h>

using namespace std;

const way[4][2]={{1,0},{0,-1},{-1,0},{0,1}};

int m,n,p;
char map[15][15];
bool check[15][15];
bool flag,fflag;
char word[150][300];

void init()
{
    int i,j;
    cin>>n>>m>>p;
    for(i=1;i<=n;i++)
        for(j=1;j<=m;j++) cin>>map[i][j];
    for(i=1;i<=p;i++) cin>>word[i];
    fflag=false;
}

void find(int x,int y,int d,int l)
{
    int i,xx,yy;
    if(flag) return;
    check[x][y]=true;
    if(l==strlen(word[d])+1)
    {
        flag=true;
        return;
    }
    for(i=0;i<=3;i++)
    {
        xx=x+way[i][0];
        yy=y+way[i][1];
        if(map[xx][yy]==word[d][l-1] && !check[xx][yy])
            find(xx,yy,d,l+1);
    }
    if(flag) return;
    check[x][y]=false;
    return;
}


void out()
{
    int i,j,l;
    char w;
    char ans[300],*p;
    p=ans;
    for(i=1;i<=n;i++)
        for(j=1;j<=m;j++)
            if(!check[i][j])
                *(p++)=map[i][j];
    *p='\0';
    l=strlen(ans);
    for(i=l-1;i>=0;i--)
        for(j=0;j<=i-1;j++)
            if(ans[j]>ans[j+1])
            {
                w=ans[j];
                ans[j]=ans[j+1];
                ans[j+1]=w;
            }
    cout<<ans<<endl;
}


void search(int x)
{
    bool check1[15][15];
    int i,j;
    if(x==p+1)
    {
        out();
        fflag=true;
    }
    if(fflag) return;
    for(i=1;i<=n;i++)
        for(j=1;j<=m;j++)
            if(map[i][j]==word[x][0] && !check[i][j])
            {
                memmove(check1,check,sizeof(check));
                flag=false;
                find(i,j,x,2);
                if(flag) search(x+1);
                memmove(check,check1,sizeof(check1));
            }
}



void work()
{
    memset(check,false,sizeof(check));
    search(1);
}



int main()
{
    init();
    work();
    return 0;
}

I think there is no trick in this test.
There is more simple solution (only 15 strings code)...
Try to find it!