题解 | 实时社交媒体热点追踪

import sys
from collections import deque, defaultdict
n = int(input())
cnt = defaultdict(lambda: 0)
dq = deque()
for line in sys.stdin:
    strs = line.strip().split()
    if n == 0:
        print("null")
        continue
    for s in strs:
        # 注意只有新关键词才需要加入队列
        if s not in cnt:
            dq.append(s)
        cnt[s] += 1
    res = []
    i = 0
    while i < n and dq:
        s = dq.popleft()
        if s in cnt:
            res.append(f'{s} {cnt[s]}')
            cnt.pop(s)
            i += 1
    if i == 0:
        print('null')
    else:
        print(' '.join(res))

 注意只有新关键词才需要加入队列