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题目：（困难）

标签：哈希表、二分查找

解法一：

class Solution:    _MOD = 2 ** 32    def longestDupSubstring(self, S: str) -> str:        def check(v):            now = 0            for i in range(v):                now = (26 * now + nums[i]) % self._MOD            count = {
   now}            max_bit = pow(26, v, self._MOD)            for i in range(size - v):                now = (now * 26 - nums[i] * max_bit + nums[i + v]) % self._MOD                if now in count:                    return i + 1                count.add(now)            return -1        size = len(S)        nums = [ord(S[i]) - 97 for i in range(size)]        start = -1        left, right = 0, size        while left < right:            mid = (left + right) // 2            res = check(mid)            print(mid, ":", res)            if res != -1:                start = res                left = mid + 1            else:                right = mid        return S[start:start + left - 1] if start != -1 else ""

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