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static int countRectangles(int[][] matrix) {
        int count = 0;
        boolean counted = false;
 
        for(int n=0; n<matrix.length; n++) { //rows
            for(int m=0; m<matrix.length; m++) { //columns
 
                counted = false;
 
                //rectangle found. detect its borders.
                if(matrix[n][m] == 1) {
                    //rectangle cells set to -1, to avoid double-calculating.
                    matrix[n][m] = -1;
                    int tempM = m,
                        tempN = n,
                        cols = 1; //count of columns in the rectangle
 
                    B: while(counted==false) {
 
                        if( ((tempM+1) < matrix.length) && (matrix[n][tempM+1]== 1) )
                            {
                                matrix[n][tempM+1] = -1;
                                cols++;
                                tempM++;
                                continue B;
                            }
 
                        if( ((tempN+1) < matrix.length) && (matrix[tempN+1][m]== 1) )
                            {
                                for(int k=0; k<cols; k++) {
                                    matrix[tempN+1][m+k]= -1;
                                }
                                tempN++;
                                continue B;
                            }
                        counted = true;     //all cells of the rectangle found.
                    }
 
                    count++;
                }
            }
        }
        return count;
    }