[Algorithm] '좋은 수' 구하기

[hwangJi-dev]

https://www.acmicpc.net/problem/1253

import sys
input = sys.stdin.readline

N = int(input())
arr = list(map(int, input().split()))
arr.sort()
ans = 0

for i in range(N):
    key = arr[i]
    p1, p2 = 0, N - 1

    while p1 < p2:
        if arr[p1] + arr[p2] == key:
            if p1 != i and p2 != i:
                ans += 1
                break
            elif p1 == i:
                p1 += 1
            elif p2 == i:
                p2 -= 1
        elif arr[p1] + arr[p2] < key:
            p1 += 1
        else:
            p2 -= 1

print(ans)