Rotate N x N matrix in 90 degrees, in place.

 void rotate90(int** Mat, int N) {
    bool* visited = new bool[N*N];
    memset(visited, 0, sizeof(bool) * N * N);
    for (int row = 0; row < N; row++) {
        for (int col = 0; col < N; col++) {
            //Mat[row][col]         -> Mat[col][N-1-row]
            //Mat[col][N-1-row]     -> Mat[N-1-row][N-1-col]
            //Mat[N-1-row][N-1-col] -> Mat[N-1-col][row]
            //Mat[N-1-col][row]     -> Mat[row][col]
            if (visited[row*N + col]) continue;

            int temp = Mat[row][col];
            Mat[row][col] = Mat[N - 1 - col][row];
            Mat[N - 1 - col][row] = Mat[N - 1 - row][N - 1 - col];
            Mat[N - 1 - row][N - 1 - col] = Mat[col][N - 1 - row];
            Mat[col][N - 1 - row] = temp;
            visited[row*N + col] = true;
            visited[(N - 1 - col)*N +row] = true;
            visited[(N - 1 - row)*N + N - 1 - col] = true;
            visited[(col)*N + N - 1 - row] = true;
        }
    }
}