Skip to main content

91. Decode Ways | Leetcode Solution

 91Decode Ways

A message containing letters from A-Z can be encoded into numbers using the following mapping:

'A' -> "1"
'B' -> "2"
...
'Z' -> "26"

To decode an encoded message, all the digits must be grouped then mapped back into letters using the reverse of the mapping above (there may be multiple ways). For example, "11106" can be mapped into:

  • "AAJF" with the grouping (1 1 10 6)
  • "KJF" with the grouping (11 10 6)

Note that the grouping (1 11 06) is invalid because "06" cannot be mapped into 'F' since "6" is different from "06".

Given a string s containing only digits, return the number of ways to decode it.

The test cases are generated so that the answer fits in a 32-bit integer.

 

Example 1:

Input: s = "12"
Output: 2
Explanation: "12" could be decoded as "AB" (1 2) or "L" (12).

Example 2:

Input: s = "226"
Output: 3
Explanation: "226" could be decoded as "BZ" (2 26), "VF" (22 6), or "BBF" (2 2 6).

Example 3:

Input: s = "06"
Output: 0
Explanation: "06" cannot be mapped to "F" because of the leading zero ("6" is different from "06").

 

Constraints:

  • 1 <= s.length <= 100
  • s contains only digits and may contain leading zero(s).

solution:

class Solution {
public:
     
     vector<int>dp{vector<int>(101, -1)};
    int decode(string s , int &sum , int n , int i)
    {     
        
       
        if(i > n)
            return 0;
          if(i == n || s.length() == 1)
        {
              if(s[i] == '0')
                  return 0;
             return 1;
        }
          
         if(dp[i] != -1)
            return dp[i];
        
        
            if(s[i] == '0')
            {
               return 0;
            }
        else
        if(s[i] == '1' )
        {   
            return dp[i]= decode(s , sum , n , i+1) + decode(s , sum , n , i+2);
            
            
        }
        else
        if(s[i] == '2')
        { 
            
            if(s[i+1] >='0' && s[i+1] <= '6')
            return dp[i] =  decode(s , sum , n, i+1)+ decode(s , sum , n, i+2);
            else
             return dp[i] = decode(s , sum , n, i+1);
        }
        else
        {
          return  dp[i] = decode(s , sum , n, i+1);
        }
        
        return  sum;

    }
    int numDecodings(string s) {
        
        int sum =0;
        int i =0;
        int n = s.length();
        return decode(s , sum , n , i);
        
    }
};

Comments

Popular posts from this blog

leetcode 48 solution

  48 .  Rotate Image You are given an  n x n  2D  matrix  representing an image, rotate the image by  90  degrees (clockwise). You have to rotate the image  in-place , which means you have to modify the input 2D matrix directly.  DO NOT  allocate another 2D matrix and do the rotation.   Example 1: Input: matrix = [[1,2,3],[4,5,6],[7,8,9]] Output: [[7,4,1],[8,5,2],[9,6,3]] Example 2: Input: matrix = [[5,1,9,11],[2,4,8,10],[13,3,6,7],[15,14,12,16]] Output: [[15,13,2,5],[14,3,4,1],[12,6,8,9],[16,7,10,11]]   Constraints: n == matrix.length == matrix[i].length 1 <= n <= 20 -1000 <= matrix[i][j] <= 1000 solution: class Solution { public:     void swap(int& a , int &b)     {         int c ;         c = a;         a = b;         b = c;     }     void transpose (vector<vector<int>...

2485. Find the Pivot Integer | Binary search

  Given a positive integer   n , find the   pivot integer   x   such that: The sum of all elements between  1  and  x  inclusively equals the sum of all elements between  x  and  n  inclusively. Return  the pivot integer  x . If no such integer exists, return  -1 . It is guaranteed that there will be at most one pivot index for the given input.   Example 1: Input: n = 8 Output: 6 Explanation: 6 is the pivot integer since: 1 + 2 + 3 + 4 + 5 + 6 = 6 + 7 + 8 = 21. Example 2: Input: n = 1 Output: 1 Explanation: 1 is the pivot integer since: 1 = 1. Example 3: Input: n = 4 Output: -1 Explanation: It can be proved that no such integer exist.   Constraints: 1 <= n <= 1000 Solution : class Solution { publ ic:     int pivotInteger( int n ) {         int sum = (( n )*( n + 1 ))/ 2 ;         int i = 1 ;         int j =...

Regular Expression Matching Leetcode Solution

Regular Expression Matching Given an input string s and a pattern p, implement regular expression matching with support for '.' and '*' where: '.' Matches any single character.​​​​ '*' Matches zero or more of the preceding element. The matching should cover the entire input string (not partial). Example 1: Input: s = "aa", p = "a"  Output: false  Explanation: "a" does not match the entire string "aa". Example 2: Input: s = "aa", p = "a*"  Output: true  Explanation: '*' means zero or more of the preceding element, 'a'. Therefore, by repeating 'a' once, it becomes "aa". Example 3: Input: s = "ab", p = ".*"  Output: true  Explanation: ".*" means "zero or more (*) of any character (.)". Constraints: 1 <= s.length <= 20 1 <= p.length <= 20 s contains only lowercase English letters. p contains only lowercase Englis...