zoukankan      html  css  js  c++  java
  • [LeetCode] Decode Ways(DP)

    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.

    就是要注意0的出现

    class Solution {
    public:
        int numDecodings(string s) {
            int len = s.size();
            if(len==0)
                return 0;
            vector<int> num(len,0);//第i个位置记录从s的第0个位置开始到第i个位置共有几种解码方式
            if(len>=1 && s[0]=='0')
                     return 0;
            
            num[0] = 1;
            if(len==1)
                return num[0];
                
            string s0 = s.substr(0,2);
            int d  = sToInt(s0);
            int n=0;
            if(d>10 && d<=26 &&  d!=20)
                num[1] = 2;
            else if((s[1] =='0' && (s[0]=='1'|| s[0]=='2'))||s[1]!='0')
                num[1] = num[0];
            else
                return 0;
            
            
            for(int i=2;i<len;i++){
                if(s[i-1]=='0'){
                    if(s[i]!='0'){
                        num[i] = num[i-1];
                        continue;
                    }
                    else
                        return 0;
                }
            
                s0 = s.substr(i-1,2);
                d  = sToInt(s0);
                if(s[i]=='0'){
                    if(d==10 || d==20){
                       num[i] = num[i-2];
                       continue;
                    }
                       
                   else 
                       return 0;
                }
                
                if(d>10 && d<=26 )
                    num[i] = num[i-1]+num[i-2];
                else
                    num[i] = num[i-1];
            
            
            }//end for
            return num[len-1];
        }
    private:
        int sToInt(string s){
          istringstream is(s);
          int d;
          is>>d;
          return d;
        
        }
    };
  • 相关阅读:
    oracle-Oracle试题
    webservice-WebService试题
    php-PHP试题
    xml-xml试题
    ajax-Ajax试题
    用java在客户端读取mongodb中的数据并发送至服务器
    表格标记
    HTML常用标记
    Java操作Mongodb 保存/读取java对象到/从mongodb
    Spark Streaming的编程模型
  • 原文地址:https://www.cnblogs.com/Xylophone/p/3909556.html
Copyright © 2011-2022 走看看