POJ 3675 - Telescope

Problem - Find the common area of a simple polygon & circle.
Solution - O(n). Do as the normal area of calculation, adding a circle clip. i.e., split the segment to 'outside' & 'inside'. The outside orientational area is the fan area, the inside orientational area is the same as the normal polygon.
Attention - the standard point must be the center of circle, which is different in normal area calculation - all points can be standard.
Result - 1AC.
Addtional Work - Redo the segxcircle, adding circle_clip_area, split_valid, angle_interval((-pi, pi]), DCLOCK in standard code.