161. One Edit Distance

I was thinking of DP, but it turns out quite straightforward. See the comments in the code.

1:  class Solution {  
2:  public:  
3:    bool isOneEditDistance(string s, string t) {  
4:      int ns = s.size();  
5:      int nt = t.size();  
6:      int n = min(ns, nt);  
7:      for (int i = 0; i < n; i++) {  
8:        if (s[i] != t[i]) {  
9:          if (ns == nt) return s.substr(i+1) == t.substr(i+1); // replace s[i] with t[i]  
10:          else if (ns < nt) return s.substr(i) == t.substr(i+1); // delete t[i]  
11:          else return s.substr(i+1) == t.substr(i); // delete s[i]  
12:        }  
13:      }  
14:      return abs(ns-nt) == 1; // one character long otherwise two strings are equal.  
15:    }  
16:  };