Sort according to the x coordinate from small to large, if x is the same, sort according to the y coordinate from small to large
The results are:
1 2
1 4 The third judgment, in reverse order, because x4 = 1 <= x3 = 2, then, y4> y3 can become the maximum point. It is the maximum point
2 2 The third judgment, the reverse order, because x3 = 2 <= x2 = 3, then, y3> y2 can become the maximum point. Here y3 <y2 is not a maximal point.
2 3 The second judgment, judgment in reverse order, because x2 = 2 <= x1 = 3, then, y2> y1 can become the maximum point. Is the maximum point
3 1 (the last one must be the maximum point) is the maximum point
