POJ 1154 Letter game (DFS)

#include <stdio.h>

#define MAX 22

int rows;
int columns;
char board[MAX][MAX];
//up    down   left   right
int dirs[4][2] = {-1, 0,  1, 0,  0, -1,  0, 1};
int visitedLetters[26];
int maxMoves;

void DFS(int row, int column, int moves){
int dir;
for (dir = 0; dir < 4; dir++){
int nextRow = row + dirs[dir][0];
int nextCol = column + dirs[dir][1];
int letter = board[nextRow][nextCol] - 'A';
if (nextRow < 0 || nextRow == rows || nextCol < 0 || nextCol == columns
|| visitedLetters[letter]){
continue;
}
visitedLetters[letter] = 1;
DFS(nextRow, nextCol, moves + 1);
visitedLetters[letter] = 0;
}
if (moves > maxMoves){
maxMoves = moves;
}
}

int main()
{
scanf("%d %d", &rows, &columns);
int row;
for (row = 0; row < rows; row++){
scanf("%s", board[row]);
}
visitedLetters[board[0][0] - 'A'] = 1;
DFS(0, 0, 1);
printf("%d", maxMoves);
return 0;
}