What is the time complexity of LeetCode 2023. Number of Pairs of Strings With Concatenation Equal to Target?

The Python solution on this page runs in O(n^2 \times m), where n and m are the lengths of the array `nums` and the string `target`, respectively.

What is the space complexity of LeetCode 2023. Number of Pairs of Strings With Concatenation Equal to Target?

The Python solution on this page uses O(1) auxiliary space.

Number of Pairs of Strings With Concatenation Equal to Target — LeetCode 2023 Python Solution

MediumArrayHash TableStringCounting

Problem: #2023
Pattern: Hash Map
Reading time: 2 min
Source: leetcode.com

The problem

Given an array of digit strings nums and a digit string target, return the number of pairs of indices (i, j) (where i != j) such that the concatenation of nums[i] + nums[j] equals target.

Example

Input: nums = ["777","7","77","77"], target = "7777"
Output: 4
Explanation: Valid pairs are:

Python solution

Python

class Solution:
    def numOfPairs(self, nums: List[str], target: str) -> int:
        n = len(nums)
        return sum(
            i != j and nums[i] + nums[j] == target for i in range(n) for j in range(n)
        )

Complexity

Measure	Complexity
Time	O(n^2 \times m), where n and m are the lengths of the array `nums` and the string `target`, respectively
Space	O(1) auxiliary

Pattern: Hash Map

Trade memory for time: remember what you have seen so the second pass never happens. LeetCode 2023. Number of Pairs of Strings With Concatenation Equal to Target is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Hash Table and Counting.

The hash map guide has the Python template for the pattern and the 709 LeetCode problems that use it.

Frequently asked questions

How hard is LeetCode 2023. Number of Pairs of Strings With Concatenation Equal to Target?: LeetCode 2023. Number of Pairs of Strings With Concatenation Equal to Target is rated Medium on LeetCode.
What is the time complexity of LeetCode 2023. Number of Pairs of Strings With Concatenation Equal to Target?: The Python solution on this page runs in O(n^2 \times m), where n and m are the lengths of the array `nums` and the string `target`, respectively.
What is the space complexity of LeetCode 2023. Number of Pairs of Strings With Concatenation Equal to Target?: The Python solution on this page uses O(1) auxiliary space.
What topics does LeetCode 2023. Number of Pairs of Strings With Concatenation Equal to Target cover?: LeetCode 2023. Number of Pairs of Strings With Concatenation Equal to Target is tagged Array, Hash Table, String and Counting on LeetCode.