OneEditDistance.java

package com.fishercoder.solutions;

/**Given two strings S and T, determine if they are both one edit distance apart.*/
public class OneEditDistance {

    public static boolean isOneEditDistance(String s, String t) {
        char[] schar = s.toCharArray();
        char[] tchar = t.toCharArray();
        
        if(Math.abs(s.length() - t.length()) == 1){
            char[] longer = (s.length() > t.length()) ? schar : tchar;
            char[] shorter = (longer == schar) ? tchar : schar;
            
            int diffCnt = 0, i = 0, j = 0;
            for(; i < shorter.length && j < longer.length;){
                if(longer[j] != shorter[i]){
                    diffCnt++;
                    j++;
                } else {
                    i++;
                    j++;
                }
            }
            return diffCnt == 1 || diffCnt == 0;//it could be the last char of the longer is the different one, in that case, diffCnt remains to be zero
        } else if(s.length() == t.length()) {
            int diffCnt = 0;
            for(int i = 0; i < s.length(); i++){
                if(schar[i] != tchar[i]) {
                    diffCnt++;
                }
                if(diffCnt > 1) return false;
            }
            return diffCnt == 1;
        }
        return false;
    }
    
    public static void main(String...strings){
        String s = "a";
        String t = "ac";
        System.out.println(isOneEditDistance(s, t));
    }

}