README_EN.md

859. Buddy Strings

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Description

Given two strings a and b, return true if you can swap two letters in a so the result is equal to b, otherwise, return false.

Swapping letters is defined as taking two indices i and j (0-indexed) such that i != j and swapping the characters at a[i] and a[j].

• For example, swapping at indices 0 and 2 in "abcd" results in "cbad".

 

Example 1:

Input: a = "ab", b = "ba"
Output: true
Explanation: You can swap a[0] = 'a' and a[1] = 'b' to get "ba", which is equal to b.

Example 2:

Input: a = "ab", b = "ab"
Output: false
Explanation: The only letters you can swap are a[0] = 'a' and a[1] = 'b', which results in "ba" != b.

Example 3:

Input: a = "aa", b = "aa"
Output: true
Explanation: You can swap a[0] = 'a' and a[1] = 'a' to get "aa", which is equal to b.

Example 4:

Input: a = "aaaaaaabc", b = "aaaaaaacb"
Output: true

 

Constraints:

• 1 <= a.length, b.length <= 2 * 104
• a and b consist of lowercase letters.

Solutions

Python3

class Solution:
    def buddyStrings(self, s: str, goal: str) -> bool:
        m, n = len(s), len(goal)
        if m != n:
            return False
        diff = sum(1 for i in range(n) if s[i] != goal[i])
        cnt1, cnt2 = Counter(s), Counter(goal)
        if cnt1 != cnt2:
            return False
        return diff == 2 or (diff == 0 and any(e > 1 for e in cnt1.values()))

Java

class Solution {
    public boolean buddyStrings(String s, String goal) {
        int m = s.length(), n = goal.length();
        if (m != n) {
            return false;
        }
        int diff = 0;
        int[] cnt1 = new int[26];
        int[] cnt2 = new int[26];
        for (int i = 0; i < n; ++i) {
            int a = s.charAt(i), b = goal.charAt(i);
            ++cnt1[a - 'a'];
            ++cnt2[b - 'a'];
            if (a != b) {
                ++diff;
            }
        }
        boolean f = false;
        for (int i = 0; i < 26; ++i) {
            if (cnt1[i] != cnt2[i]) {
                return false;
            }
            if (cnt1[i] > 1) {
                f = true;
            }
        }
        return diff == 2 || (diff == 0 && f);
    }
}

C++

class Solution {
public:
    bool buddyStrings(string s, string goal) {
        int m = s.size(), n = goal.size();
        if (m != n) return false;
        int diff = 0;
        vector<int> cnt1(26);
        vector<int> cnt2(26);
        for (int i = 0; i < n; ++i)
        {
            ++cnt1[s[i] - 'a'];
            ++cnt2[goal[i] - 'a'];
            if (s[i] != goal[i]) ++diff;
        }
        bool f = false;
        for (int i = 0; i < 26; ++i)
        {
            if (cnt1[i] != cnt2[i]) return false;
            if (cnt1[i] > 1) f = true;
        }
        return diff == 2 || (diff == 0 && f);
    }
};

Go

func buddyStrings(s string, goal string) bool {
	m, n := len(s), len(goal)
	if m != n {
		return false
	}
	diff := 0
	cnt1 := make([]int, 26)
	cnt2 := make([]int, 26)
	for i := 0; i < n; i++ {
		cnt1[s[i]-'a']++
		cnt2[goal[i]-'a']++
		if s[i] != goal[i] {
			diff++
		}
	}
	f := false
	for i := 0; i < 26; i++ {
		if cnt1[i] != cnt2[i] {
			return false
		}
		if cnt1[i] > 1 {
			f = true
		}
	}
	return diff == 2 || (diff == 0 && f)
}

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