백준 1987번 C++ 풀이

#include <iostream>
#include <algorithm>
#include <queue>
#include <climits>
#include <string>
#include <map>
using namespace std;
int r, c;
bool isVisited[21][21];
char buffer[21][21];
bool isCharVisited[30];
int delta[4][2] = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
int maxNumber = 0;
void dfs(int x, int y, int number){
    maxNumber = max(maxNumber, number);
    for (auto i=0; i<4; i++){
        int nextX = x + delta[i][0];
        int nextY = y + delta[i][1];
        if ( 0 <= nextX && nextX < c && 0 <= nextY && nextY <r){
            if (!isVisited[nextX][nextY]){
                char temp = buffer[nextX][nextY];
                int index = temp - 'A';
                if (!isCharVisited[index]){
                    isCharVisited[index] = true;
                    isVisited[nextX][nextY] = true;
                    dfs(nextX, nextY, number+1);
                    isCharVisited[index] = false;
                    isVisited[nextX][nextY] = false;
                }

            }
        }
    }
}
int main(){
    cin.tie(NULL);
    ios::sync_with_stdio(false);
    cin >> r >> c;
    for (auto y=0; y<r; y++){
        for (auto x=0; x<c; x++){
            cin >> buffer[x][y];
        }
    }
    isCharVisited[buffer[0][0]-'A'] = true;
    isVisited[0][0]= true;
    dfs(0,0,0);
    cout << maxNumber + 1;
    return 0;
}