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2023. Number of Pairs of Strings With Concatenation Equal to Target

Difficulty Topics

Description

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 1:

Input: nums = ["777","7","77","77"], target = "7777"
Output: 4
Explanation: Valid pairs are:
- (0, 1): "777" + "7"
- (1, 0): "7" + "777"
- (2, 3): "77" + "77"
- (3, 2): "77" + "77"

Example 2:

Input: nums = ["123","4","12","34"], target = "1234"
Output: 2
Explanation: Valid pairs are:
- (0, 1): "123" + "4"
- (2, 3): "12" + "34"

Example 3:

Input: nums = ["1","1","1"], target = "11"
Output: 6
Explanation: Valid pairs are:
- (0, 1): "1" + "1"
- (1, 0): "1" + "1"
- (0, 2): "1" + "1"
- (2, 0): "1" + "1"
- (1, 2): "1" + "1"
- (2, 1): "1" + "1"

 

Constraints:

  • 2 <= nums.length <= 100
  • 1 <= nums[i].length <= 100
  • 2 <= target.length <= 100
  • nums[i] and target consist of digits.
  • nums[i] and target do not have leading zeros.

Solution

number-of-pairs-of-strings-with-concatenation-equal-to-target.py
class Solution:
    def numOfPairs(self, nums: List[str], target: str) -> int:
        n = len(nums)
        t = len(target)
        prefix = set()
        res = 0

        for i in range(1, t):
            prefix.add(target[:i])

        for i, word1 in enumerate(nums):
            if word1 in prefix:
                for j, word2 in enumerate(nums):
                    if i != j and word1 + word2 == target:
                        res += 1

        return res