Sword finger offer 46 Translate numbers to strings (DP)

The finger of the sword Offer 46. Translate numbers into strings

• The number composed of the current character and the previous character is in the interval [10,25] Inside , The current character can be translated together with the previous character （ Add two characters to the last translation result ）, It can also be translated separately （ Add the translation result of the current character to the last translation result ）, namely ：$dp[i]=dp[i-2]+dp[i-1]$
• The number composed of the current character and the previous character is not in the range [10,25] Inside , Only the current character can be translated separately , This is to add the translation result of this character to the result of the last translation , The quantity is the same as the result of the previous translation , namely ：$dp[i]=dp[i-1]$

class Solution {
    
public:
    int translateNum(int num) {
    
        string str = to_string(num);
        // ans[i] Express str [0, i] There are several ways of translation 
        vector<int> ans(str.size(), 0);
        ans[0] = 1;

        for (int i = 1; i < str.size(); i++) {
    
        	//  Just think ahead of one , because z and 25（ Two digit number ） Corresponding 
            if(str[i - 1] == '1' || (str[i - 1] == '2' && str[i] <= '5')){
    
                // [10, 25]  Two digit translation 
                if (i == 1) {
    
                	//  The current character can be translated with the previous character ,i=1 when , At this time, the translation results of the previous round will be taken , Causing the visit to cross the border 
                	//  there 1 Represents the result of joint translation with the previous character 
                    ans[i] = ans[i - 1] + 1;
                    continue;
                }
                ans[i] = ans[i - 1] + ans[i - 2];
            }
            else {
    
                ans[i] = ans[i - 1];
            }
        }
        return ans[str.size() - 1];
    }
};