Last updated on October 6th, 2024 at 02:02 pm
Here, We see Decode Ways II LeetCode Solution. This Leetcode problem is done in many programming languages like C++, Java, JavaScript, Python, etc. with different approaches.
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Topics
Dynamic Programming
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Level of Question
Hard
Decode Ways II LeetCode Solution
Table of Contents
Problem Statement
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".
In addition to the mapping above, an encoded message may contain the '*' character, which can represent any digit from '1' to '9' ('0' is excluded). For example, the encoded message "1*" may represent any of the encoded messages "11", "12", "13", "14", "15", "16", "17", "18", or "19". Decoding "1*" is equivalent to decoding any of the encoded messages it can represent.
Given a string s consisting of digits and '*' characters, return the number of ways to decode it.
Since the answer may be very large, return it modulo 109 + 7.
Example 1:
Input: s = “*”
Output: 9
Explanation: The encoded message can represent any of the encoded messages “1”, “2”, “3”, “4”, “5”, “6”, “7”, “8”, or “9”. Each of these can be decoded to the strings “A”, “B”, “C”, “D”, “E”, “F”, “G”, “H”, and “I” respectively.
Hence, there are a total of 9 ways to decode “*”.
Example 2:
Input: s = “1*”
Output: 18
Explanation: The encoded message can represent any of the encoded messages “11”, “12”, “13”, “14”, “15”, “16”, “17”, “18”, or “19”. Each of these encoded messages have 2 ways to be decoded (e.g. “11” can be decoded to “AA” or “K”).
Hence, there are a total of 9 * 2 = 18 ways to decode “1*”.
Example 3:
Input: s = “2*”
Output: 15
Explanation: The encoded message can represent any of the encoded messages “21”, “22”, “23”, “24”, “25”, “26”, “27”, “28”, or “29”. “21”, “22”, “23”, “24”, “25”, and “26” have 2 ways of being decoded, but “27”, “28”, and “29” only have 1 way.
Hence, there are a total of (6 * 2) + (3 * 1) = 12 + 3 = 15 ways to decode “2*”.
1. Decode Ways II LeetCode Solution C++
class Solution {
public:
int MOD = 1e9+7;
int dp[100001];
int helper(int ind, string &s){
if(ind == s.size()){
return 1;
}
if(s[ind] == '0'){
return 0;
}
if(dp[ind] != -1){
return dp[ind];
}
long long first = helper(ind+1, s);
if(s[ind] == '*'){
first = (first*9)%MOD;
}
long long second = 0;
long long third = 0;
if(ind+1 < s.size()){
if(s[ind] == '1' || s[ind] == '*'){
if(s[ind+1] == '*'){
second = helper(ind+2, s);
second = (second*9)%MOD;
}
else if(s[ind+1] != '*'){
second = helper(ind+2, s);
}
}
if(s[ind] == '2' || s[ind] == '*'){
if(s[ind+1] == '*') {
third = helper(ind+2, s);
third = (third*6)%MOD;
}
else if(s[ind+1]-'0' <= 6){
third = helper(ind+2, s);
}
}
}
return dp[ind] = ((first+second)%MOD+third)%MOD;
}
int numDecodings(string s) {
memset(dp, -1, sizeof(dp));
return helper(0, s);
}
};2. Decode Ways II LeetCode Solution Java
class Solution {
public int numDecodings(String s) {
if (s == null) {
throw new IllegalArgumentException("Input string is null");
}
if (s.length() == 0 || s.charAt(0) == '0') {
return 0;
}
long pre = 1; // dp[i-2]
long cur = s.charAt(0) == '*' ? 9 : 1;
for (int i = 1; i < s.length(); i++) {
long sum = 0; // dp[i]
char curChar = s.charAt(i);
char preChar = s.charAt(i - 1);
if (curChar != '0') {
sum = cur * (curChar == '*' ? 9 : 1);
}
if (preChar == '*') {
if (curChar == '*') {
sum += pre * 15;
} else if (curChar <= '6') {
sum += pre * 2;
} else {
sum += pre;
}
} else {
if (curChar == '*') {
if (preChar == '1') {
sum += pre * 9;
} else if (preChar == '2') {
sum += pre * 6;
}
} else {
int num = Integer.parseInt(s.substring(i - 1, i + 1));
if (num >= 10 && num <= 26) {
sum += pre;
}
}
}
pre = cur;
cur = sum % 1000000007;
}
return (int) cur;
}
}3. Decode Ways II LeetCode Solution JavaScript
var numDecodings = function(s) {
let mod = 1e9 + 7;
let [e0, e1, e2, f0] = [1, 0, 0, 0];
for (const c of s) {
if (c == '*') {
f0 = 9 * e0 + 9 * e1 + 6 * e2;
e1 = e0;
e2 = e0;
} else {
f0 = (c > '0') * e0 + e1 + (c <= '6') * e2;
e1 = (c == '1') * e0;
e2 = (c == '2') * e0;
}
e0 = f0 % mod;
}
return e0;
};4. Decode Ways II LeetCode Solution Python
class Solution(object):
def numDecodings(self, S):
answer = 1
prev_answer = 1
one, two = False, False
for i in S:
if i == '*':
new = answer*9
if one:
new += 9*prev_answer
if two:
new += 6*prev_answer
one, two = True, True
else:
new = answer if (i > '0') else 0
if one:
new += prev_answer
if (two and i <= '6'):
new += prev_answer
one = (i == '1')
two = (i == '2')
prev_answer = answer
answer = new % (10**9 + 7)
return answer