1 public class Solution { 2     public boolean isOneEditDistance(String s, String t) { 3         if (s.length()==0 && t.length()==0) return false; 4         if (s.length()+t.length()==1) return true; 5          6         if (Math.abs(s.length()-t.length())>1) return false;         7  8         if (s.length()==t.length()) return isOneReplace(s,t); 9 10         if (s.length()>t.length()) return isOneInsert(s,t);11         else return isOneInsert(t,s);12         13     }14 15     public boolean isOneInsert(String a, String b){16         //a is 1 char longer than b, we determine whether a and b is one insertion distance.17 18         boolean modified = false;19 20         int index1 = 0;21         int index2 = 0;22 23         while (index2<b.length()){24             if (a.charAt(index1)==b.charAt(index2)){25                 index1++;26                 index2++;27             } else {28                 if (modified) return false;29                 else {30                     index1++;31                     modified = true;32                 }33             }34         }35         return true;36     }37 38 39     public boolean isOneReplace(String a, String b){40         //a and b have the same length, we determine whether they are one replace aparted.41         boolean modified = false;42         int index1=0;43         while (index1<a.length())44             if (a.charAt(index1)==b.charAt(index1))45                 index1++;46             else if (modified) return false;47             else {48                 index1++;49                 modified = true;50             }51         if (modified) return true;52         else return false;53     }54               55  56         57     58 }