Buddystring.java

/*859. Buddy Strings
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Easy
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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.
 

Constraints:

1 <= s.length, goal.length <= 2 * 104
s and goal consist of lowercase letters. */

class Solution {
    public boolean buddyStrings(String s, String goal) {
        //PART 1
        if(s.length()!=goal.length())
        {
            return false;
        }

        // PART2
        if(s.equals(goal))
        {
            HashMap <Character,Integer> map=new HashMap<>();
            for(int i=0;i<s.length();i++)
            {
                map.put(s.charAt(i),map.getOrDefault(s.charAt(i),0)+1);
                if(map.get(s.charAt(i)) >= 2) 
                {
                    return true;
                }

            }
            return false;
        }

        //PART 3
        int first=-1;
        int second=-1;
        int count=0;
        for(int i=0;i<s.length();i++)
        {
            if(s.charAt(i)!=goal.charAt(i))
            {
                count++;
                if(first==-1)
                {
                    first=i;
                }
                else
                {
                    second=i;
                }
            }
        }
        if(count!=2)
        {
            return false;
        }
        return s.charAt(first) == goal.charAt(second) &&s.charAt(second) == goal.charAt(first);
               
    }
}
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//sc=o(n)