Submission #7913642

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Source Code Expand

import sys
input = sys.stdin.readline
from collections import Counter

N, M = map(int, input().split())
X = list(map(int, input().split()))


def main():
    P = [[] for _ in range(M)]

    for x in X:
        P[x%M].append(x)

    ans = 0
    checked = [False]*M
    for m in range(M):
        if checked[m]:
            continue
        if m == 0:
            ans += len(P[m])//2
        else:
            L1, L2 = len(P[m]), len(P[M-m])
            if L1 > L2:
                ans += L2
                C1 = Counter(P[m])
                n = 0
                for num, c1 in C1.items():
                    if c1 % 2 != 0:
                        n += 1
                if L2 >= n:
                    ans += (L1-L2)//2
                else:
                    ans += (L1-n)//2
            else:
                ans += L1
                C2 = Counter(P[M-m])
                n = 0
                for num, c2 in C2.items():
                    if c2 % 2 != 0:
                        n += 1
                if L1 >= n:
                    ans += (L2-L1)//2
                else:
                    ans += (L1-n)//2
            checked[m] = True
            checked[M-m] = True

    print(ans)


if __name__ == "__main__":
    main()

Submission Info

Judge Result