SRM 146 DIV1 300 長方形の中に長方形(正方形を除く)はいくつある？

RectangularGrid.java

 public long countRectangles(int width, int height) {
	long count = 0;
	count = calcCombination(width+1, 2)*calcCombination(height+1, 2);
	int short_side = Math.min(width, height);
	for (int i = 0; i <= short_side; i++) {
		count -=(width - i) * (height - i);
	}

	return count;
}

long calcCombination(int n, int m){
	if(n < m || m < 0) {
        return 0;
    }
	long c = 1;
    m = (n - m < m ? n - m : m);
    for(int ns = n - m + 1, ms = 1; ms <= m; ns ++, ms ++) {
        c *= ns;
        c /= ms;
    }
    return c;
}