[two pointers]Codeforces

http://codeforces.com/problemset/problem/1166/C

分析：给定n 个数，其中有x,y,... 满足 min(∣x−y∣,∣x+y∣) ≤ min(∣x∣,∣y∣)且 max(∣x∣,∣y∣) ≤ max(∣x−y∣,∣x+y∣)