poj1154

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简单题

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#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cstdio>
using namespace std;

#define maxn 25

int n, m;
char map[maxn][maxn];
bool vis[30];
int ans;
int dir[4][2] =
{
{ 0, 1 },
{ 1, 0 },
{ -1, 0 },
{ 0, -1 } };

bool ok(int x, int y)
{
    if (x < 0 || y < 0 || x >= n || y >= m)
        return false;
    return !vis[map[x][y] - 'A'];
}

void dfs(int x, int y, int step)
{
    ans = max(ans, step);
    vis[map[x][y] - 'A'] = true;
    for (int i = 0; i < 4; i++)
        if (ok(x + dir[i][0], y + dir[i][1]))
        {
            dfs(x + dir[i][0], y + dir[i][1], step + 1);
        }
    vis[map[x][y] - 'A'] = false;
}

int main()
{
    //freopen("t.txt", "r", stdin);
    memset(vis, 0, sizeof(vis));
    scanf("%d%d", &n, &m);
    for (int i = 0; i < n; i++)
        scanf("%s", map[i]);
    ans = 1;
    dfs(0, 0, 1);
    printf("%d\n", ans);
    return 0;
}