2840 - Check if Strings Can be Made Equal With Operations II (Medium)

Problem Link

https://leetcode.com/problems/check-if-strings-can-be-made-equal-with-operations-ii/

Problem Statement

You are given two strings s1 and s2, both of length n, consisting of lowercase English letters.

You can apply the following operation on any of the two strings any number of times:

• Choose any two indices i and j such that i < j and the difference j - i is even, then swap the two characters at those indices in the string.

Return trueif you can make the stringss1ands2equal, andfalseotherwise.

Example 1:

Input: s1 = "abcdba", s2 = "cabdab"
Output: true
Explanation: We can apply the following operations on s1:
- Choose the indices i = 0, j = 2. The resulting string is s1 = "cbadba".
- Choose the indices i = 2, j = 4. The resulting string is s1 = "cbbdaa".
- Choose the indices i = 1, j = 5. The resulting string is s1 = "cabdab" = s2.

Example 2:

Input: s1 = "abe", s2 = "bea"
Output: false
Explanation: It is not possible to make the two strings equal.

Constraints:

• n == s1.length == s2.length
• 1 <= n <= 10 ^ 5
• s1 and s2 consist only of lowercase English letters.

Approach 1: Sorting

We can only swap any characters with the same parity. We can simply sort all characters at even parity and odd parity for $s1$ and $s2$, then compare if they are all same.

C++

Written by @wingkwong

class Solution {
public:
    bool checkStrings(string s1, string s2) {
        // put all characters in s1 at even index
        // put all characters in s1 at odd index
        vector<int> s1_even, s1_odd;
        for (int i = 0; i < s1.size(); i++) {
            if (i % 2 == 0) s1_even.push_back(s1[i]);
            else s1_odd.push_back(s1[i]);
        }
        // sort them
        sort(s1_even.begin(), s1_even.end());
        sort(s1_odd.begin(), s1_odd.end());
        
        // put all characters in s2 at even index
        // put all characters in s2 at odd index
        vector<int> s2_even, s2_odd;
        for (int i = 0; i < s2.size(); i++) {
            if (i % 2 == 0) s2_even.push_back(s2[i]);
            else s2_odd.push_back(s2[i]);
        }
        // sort them
        sort(s2_even.begin(), s2_even.end());
        sort(s2_odd.begin(), s2_odd.end());

        return s1_even == s2_even && s1_odd == s2_odd;
    }
};