POJ 1154 LETTERS

题意：输入行数和列数，然后输入大写字母的矩阵，从左上角出发，只能上下左右走，求能够经过的不重复字母的最多的个数。

题解

/*
基础的dfs
*/
#include <iostream>
#include <vector>

using namespace std;

int ans, n, m;
string map[21];
int direction[4][2] = { 0, -1, -1, 0, 0, 1, 1, 0 };
int visited[30];

void dfs(int i, int j, int num)
{
    ans = max(ans, num);
    for (int k = 0; k < 4; ++k) {
        int ii = i + direction[k][0];
        int jj = j + direction[k][1];
        if ((ii < 0) || (jj < 0) || (ii >= n) || (jj >= m)) continue;
        if (visited[map[ii][jj] - 'A']) continue;
        visited[map[ii][jj] - 'A'] = 1;
        dfs(ii, jj, num + 1);
        visited[map[ii][jj] - 'A'] = 0;
    }
}

int main()
{
    for (int i = 0; i < 30; ++i) visited[i] = 0;
    cin >> n >> m;
    for (int i = 0; i < n; ++i) cin >> map[i];
    ans = 1;
    visited[map[0][0] - 'A'] = 1;
    dfs(0, 0, 1);
    cout << ans << endl;
    return 0;
}