LeetCode:Decode Ways

Posted 2020-07-13 walker lee

Decode Ways

Total Accepted: 70502 Total Submissions: 399086 Difficulty: Medium

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 could be decoded as "AB" (1 2) or "L" (12).

The number of ways decoding "12" is 2.

Subscribe to see which companies asked this question

Hide Tags

 Dynamic Programming String

c++ code:

class Solution {
public:
    int numDecodings(string s) {
        
        int n = s.size();
        if(n==0) return 0;
        
        int pre = 0;
        int cur = 1;
        
        for(int i=1;i<=n;i++) {
            if(s[i-1]=='0') cur = 0;
            if(!(s[i-2]=='1' || (s[i-2]=='2')&&(s[i-1]<='6')))
                pre = 0;
            int tmp = cur;
            cur += pre;
            pre = tmp;
        }
        return cur;
    }
};