859. Buddy Strings

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題目敘述

Given two strings s and goal, return true if you can swap two letters in s so the result is equal to goal, 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 s[i] and s[j].

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

Example 1

Input: s = “ab”, goal = “ba” Output: true Explanation: You can swap s[0] = ‘a’ and s[1] = ‘b’ to get “ba”, which is equal to goal.

Example 2

Input: s = “ab”, goal = “ab” Output: false Explanation: The only letters you can swap are s[0] = ‘a’ and s[1] = ‘b’, which results in “ba” != goal.

Example 3

Input: s = “aa”, goal = “aa” Output: true Explanation: You can swap s[0] = ‘a’ and s[1] = ‘a’ to get “aa”, which is equal to goal.

解題思路

Solution

import java.util.HashSet;
import java.util.Set;

class Solution {
    public boolean buddyStrings(String s, String goal) {
        int n = s.length();
        
        if (s.equals(goal)) {
            Set<Character> temp = new HashSet<>();
            for (char c : s.toCharArray()) {
                temp.add(c);
            }
            return temp.size() < goal.length(); // Swapping same characters
        } // two string equal

        int i = 0;
        int j = n - 1;

        while (i < j && s.charAt(i) == goal.charAt(i)) {
            i++;
        }

        while (j >= 0 && s.charAt(j) == goal.charAt(j)) {
            j--;
        }

        if (i < j) {
            char[] clone = s.toCharArray();
            char temp = clone[i];
            clone[i] = clone[j];
            clone[j] = temp;
            s = new String(clone);
        } // Find two letter to swap, when two letter on deference string in same index isn't equal

        return s.equals(goal);
    }
}