LongChallenge(Sep) - Full Editorial

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ROTATPOL - Editorial

PROBLEM LINK: Practice Div-2 Contest Div-1 Contest Author: tautsjasiunsas Tester: alei_adm Editorialist: tautsjasiunsas DIFFICULTY: MEDIUM-HARD? PREREQUISITES: Geometry, 2-pointers PROBLEM: Given a polyline P, find a direction v such that all indices i with v \cdot (P_{i+1}-P_i) > 0 form a subsegment and none are equal to 0. QUICK EXPLANATION: First, create an array A_i = P_i- P_{i+1}. After, make a vector S storing all A_i, -A_i, (0,1), (0,-1), (1,0), (-1,0). Sort S by polar angle…