Submission #7458787

---

Source Code Expand

from collections import defaultdict
N,M=map(int,input().split())
X=list(map(int,input().split()))
tab=[0]*M
cnts=[defaultdict(lambda: 0) for _ in range(M)]
for x in X:
    tab[x%M]+=1
    cnts[x%M][x]+=1

ans=0
for i in range(M//2+1):
    if i==0 or (M%2==0 and i==M//2):
        npair = tab[i]//2
        tab[i]-=npair
        ans += npair
    else:
        npair = min(tab[i],tab[M-i])
        tab[i]-=npair
        tab[M-i]-=npair
        ans += npair

for remn, d in zip(tab, cnts):
    tmp=0
    for _,n in d.items():
        tmp += (n//2)
    ans += min(tmp, remn//2)

print(ans)

Submission Info

Judge Result