Detect Cycles in 2D Grid LeetCode solution in C++

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class Solution {
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 public:
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  int dx[4] = {-1, 1, 0, 0};
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  int dy[4] = {0, 0, 1, -1};
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  bool solve(vector<vector<char>> &grid, int i, int j, int m, int n, int x, int y,
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             vector<vector<int>> &vis, char startChar) {
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    vis[i][j] = 1;
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    for (int k = 0; k < 4; k++) {
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      int xx = i + dx[k];
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      int yy = j + dy[k];
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      if (xx >= 0 && yy >= 0 && xx < m && yy < n && grid[xx][yy] == startChar &&
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          !(x == xx && y == yy)) {
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        if (vis[xx][yy] || solve(grid, xx, yy, m, n, i, j, vis, startChar)) return true;
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      }
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    }
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    return false;
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  }
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  bool containsCycle(vector<vector<char>> &grid) {
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    int m = grid.size();
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    int n = grid[0].size();
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    vector<vector<int>> vis(m, vector<int>(n, 0));
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    for (int i = 0; i < m; i++) {
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      for (int j = 0; j < n; j++) {
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        if (!vis[i][j] && solve(grid, i, j, m, n, -1, -1, vis, grid[i][j])) {
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          return true;
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        }
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      }
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    }
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    return false;
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  }
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};