Thinking process

public class Solution {
    public boolean isOneEditDistance(String s, String t) {
        if (Math.abs(s.length() - t.length()) > 1) return false;
        if (s.length() == t.length()) {
            int diff = 0;
            for (int i = 0; i < s.length(); ++i) {
                if (s.charAt(i) != t.charAt(i)) {
                    diff++;
                }
            }

            if (diff == 1) return true;
        } else {
            return (s.length() > t.length()) ? isOneInsert(s, t) : isOneInsert(t, s);
        }

        return false;
    }

    private boolean isOneInsert (String s, String t) {
        int diff = 0;
        int i = 0, j = 0;
        while (j < t.length() && i < s.length()) {
            if (s.charAt(i) == t.charAt(j)) {
                i++;
                j++;
            } else {
                diff++;
                i++;
            }
        }

        return diff <= 1;
    }
}