Submission #10528254

---

Source Code Expand

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

def main():
    N,M = map(int,input().split())
    x = list(map(int,input().split()))
    
    ml = [[] for _ in range(M)]
    for num in x:
        ml[num%M].append(num)

    cl = [[0,0] for _ in range(M)]
    for i in range(M):
        y = ml[i]
        c = tuple(Counter(y).values())
        for num in c:
            cl[i][0] += num//2*2
            cl[i][1] += num%2

    ans = (cl[0][0]+cl[0][1])//2
    for i in range(1,-(-M//2)):
        da,oa = cl[i]
        db,ob = cl[M-i]
        num = 0
        if oa >= ob:
            num += (ob+min(oa-ob,db)+max(0,db-(oa-ob))//2+da//2)
        else:
            num += (oa+min(ob-oa,da)+max(0,da-(ob-oa))//2+db//2)
        ans += num
    
    if M%2 == 0:
        m = M//2
        ans += (cl[m][0]+cl[m][1])//2
        
    print(ans)

if __name__ == "__main__":
    main()

Submission Info

Judge Result