[LeetCode] 91. Decode Ways

[LeetCode] 91. Decode Ways

Question

A message containing letters from A-Z is being encoded to numbers using the following mapping:

'A'-> 1
'B'-> 2
...
'Z'-> 26
Given an encoded message containing digits, determine the total number of ways to decode it.

For example,
Given encoded message "12", it cocould be decoded as "AB" (1 2) or "L" (12 ).

The number of ways decoding "12" is 2.

Analysis

Code

/* ------------------------------------- * Date: 2015-06-23 * Author: SJF0115 * Subject: 91. Decode Ways * URL: Response result: AC * Source: LeetCode * blog: Example */# include
  
   
Using namespace std; class Solution {public: int numDecodings (string s) {int size = s. size (); if (s [0] = '0') {return 0;} // if (size = 0 | size = 1) {return size;} // if int pre = 1, cur = 1, res; for (int I = 1; I <size; ++ I) {if (isValid (s [I-1], s [I]) & isValid (s [I]) {res = pre + cur;} // if else if (! IsValid (s [I-1], s [I]) & isValid (s [I]) {res = cur ;} // else if (isValid (s [I-1], s [I]) &! IsValid (s [I]) {res = pre;} // else {return 0;} // else pre = cur; cur = res ;} // for return res;} private: bool isValid (char pre, char cur) {if (pre = '1' | (pre = '2' & cur <= '6') {return true;} // if return false ;} bool isValid (char cur) {if (cur> = '1' & cur <= '9') {return true ;}// if return false ;}}; int main () {Solution s; string str ("1202111110"); cout <
   
  

Running time

Idea 2-Timeout

/* ------------------------------------- * Date: 2015-06-21 * Author: SJF0115 * Subject: 91. Decode Ways * URL: Expiration result: timeout * Source: LeetCode * blog: expiration */# include  Using namespace std; class Solution {public: int numDecodings (string s) {int size = s. size (); if (size = 0 | size = 1) {return size;} // if int index =-1; int count = 0; helper (s, index, count, ""); return count;} private: void helper (string & s, int index, int & count, string word) {int size = s. size (); if (index = size-1) {++ count; cout <"word->" <  0) {word + = ('A' + num-1); helper (s, index + I, count, word); word. erase (word. size ()-1) ;}// if else {break ;}// if} // for }}; int main () {Solution s; string str ("1234"); cout <