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.
public class Solution { public int numDecodings(String s) { // Start typing your Java solution below // DO NOT write main() function ArrayList<Integer> solutions = new ArrayList<Integer>(); if(s.length()!= 0){ recursion(s,solutions); } return solutions.size(); } public void recursion(String s,ArrayList<Integer> solutions ){ if(s.length() == 0){ solutions.add(1); } else{ int value = Character.getNumericValue(s.charAt(0)); if(value >0 && value <=9){ recursion(s.substring(1),solutions); } if(s.length() >=2){ int value1 = Character.getNumericValue(s.charAt(0)); int value2 = Character.getNumericValue(s.charAt(1)); if(value1 == 1 && value2 >=0 && value2 <=9){//value1 is 1 recursion(s.substring(2),solutions); } if(value1 == 2 && value2 >=0 && value2 <=6){//value1 is 2 two conditions recursion(s.substring(2),solutions); } } } } }
mistake: Character.getNumericValue(s.charAt(0)); character to get int from string
public class Solution { public int numDecodings(String s) { if(s.length() == 0) return 0; int[] num = new int[2]; num[0] = 1; // decode the first two integers num[1] = 1; // decode the first integer for(int i = 0 ; i < s.length();i++){ int temp = 0; if(s.charAt(i) != '0') temp += num[1]; if(i>0){ int a = Integer.parseInt(s.substring(i-1,i+1)); if(s.charAt(i-1) !='0' && a>=1 && a<=26){ temp+= num[0]; } } num[0] = num[1]; num[1] = temp; } return num[1]; } }
learned: return num[1] , like clim stairs temp is total decode ways for s.substring(0,2)