四个词各出现几次

四个要找的词 he、she、his、hers，一段文本 ushershishe（11 个字符，下标从 0 起）：按 WORDS 里的顺序，输出四个词各自的出现次数：

WORDS = ['he', 'she', 'his', 'hers']
TXT = "ushershishe"

def build(words):
    t = {}
    for w in words:
        node = t
        for ch in w:
            node = node.setdefault(ch, {})
        node["#"] = w
    return t

def scan(t, txt):
    """从每个起点顺着 Trie 往下走，走到 # 就记一个命中"""
    hits = []
    for i in range(len(txt)):
        node = t
        for j in range(i, len(txt)):
            if txt[j] not in node:
                break
            node = node[txt[j]]
            if "#" in node:
                hits.append((i, node["#"]))
    return sorted(hits)

t = build(WORDS)
hits = scan(t, TXT)
print("/".join(str(sum(1 for _, w in hits if w == x)) for x in WORDS))