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Posts tagged as “kmp”

花花酱 LeetCode 1764. Form Array by Concatenating Subarrays of Another Array

You are given a 2D integer array groups of length n. You are also given an integer array nums.

You are asked if you can choose n disjoint subarrays from the array nums such that the ith subarray is equal to groups[i] (0-indexed), and if i > 0, the (i-1)th subarray appears before the ith subarray in nums (i.e. the subarrays must be in the same order as groups).

Return true if you can do this task, and false otherwise.

Note that the subarrays are disjoint if and only if there is no index k such that nums[k] belongs to more than one subarray. A subarray is a contiguous sequence of elements within an array.

Example 1:

Input: groups = [[1,-1,-1],[3,-2,0]], nums = [1,-1,0,1,-1,-1,3,-2,0]
Output: true
Explanation: You can choose the 0th subarray as [1,-1,0,1,-1,-1,3,-2,0] and the 1st one as [1,-1,0,1,-1,-1,3,-2,0].
These subarrays are disjoint as they share no common nums[k] element.

Example 2:

Input: groups = [[10,-2],[1,2,3,4]], nums = [1,2,3,4,10,-2]
Output: false
Explanation: Note that choosing the subarrays [1,2,3,4,10,-2] and [1,2,3,4,10,-2] is incorrect because they are not in the same order as in groups.
[10,-2] must come before [1,2,3,4].

Example 3:

Input: groups = [[1,2,3],[3,4]], nums = [7,7,1,2,3,4,7,7]
Output: false
Explanation: Note that choosing the subarrays [7,7,1,2,3,4,7,7] and [7,7,1,2,3,4,7,7] is invalid because they are not disjoint.
They share a common elements nums[4] (0-indexed).


  • groups.length == n
  • 1 <= n <= 103
  • 1 <= groups[i].length, sum(groups[i].length) <= 103
  • 1 <= nums.length <= 103
  • -107 <= groups[i][j], nums[k] <= 107

Solution: Brute Force

Time complexity: O(n^2?)
Space complexity: O(1)


KMP Algorithm SP19

KMP Algorithm, KMP 字符串搜索算法

Time complexity: O(m+n)
Space complexity: O(m)





LeetCode 28. strStr()


LeetCode 459. Repeated Substring Pattern


1392. Longest Happy Prefix


花花酱 LeetCode 1392. Longest Happy Prefix

A string is called a happy prefix if is a non-empty prefix which is also a suffix (excluding itself).

Given a string s. Return the longest happy prefix of s .

Return an empty string if no such prefix exists.

Example 1:

Input: s = "level"
Output: "l"
Explanation: s contains 4 prefix excluding itself ("l", "le", "lev", "leve"), and suffix ("l", "el", "vel", "evel"). The largest prefix which is also suffix is given by "l".

Example 2:

Input: s = "ababab"
Output: "abab"
Explanation: "abab" is the largest prefix which is also suffix. They can overlap in the original string.

Example 3:

Input: s = "leetcodeleet"
Output: "leet"

Example 4:

Input: s = "a"
Output: ""


  • 1 <= s.length <= 10^5
  • s contains only lowercase English letters.

Solution: Rolling Hash

Time complexity: O(n) / worst case: O(n^2)
Space complexity: O(1)