**Decode Message - Amazon Top Interview Questions**

### Problem Statement :

Given the mapping "a" = 1, "b" = 2, ... "z" = 26, and an encoded message message (as a string), count the number of ways it can be decoded. Constraints n ≤ 100,000 where n is the length of message Example 1 Input message = "111" Output 3 Explanation This can be decoded 3 ways: aaa, ak, and ka. Example 2 Input message = "8" Output 1 Explanation This can be only decoded one way, as h. Example 3 Input message = "12" Output 2 Explanation This can be decoded 2 ways: ab or l. Example 4 Input message = "60" Output 0 Explanation There's no way to decode this message. Example 5 Input message = "0012" Output 0

### Solution :

` ````
Solution in C++ :
int solve(string s) {
int n = s.size();
long int dp[n + 1];
memset(dp, 0, sizeof(dp));
if (s[0] != '0') dp[1] = 1;
dp[0] = 1;
for (int i = 2; i <= n; i++) {
if (s[i - 1] > '0') dp[i] = dp[i - 1];
if (s[i - 2] == '1' || (s[i - 2] == '2' && s[i - 1] <= '6')) dp[i] += dp[i - 2];
}
return dp[n];
}
```

` ````
Solution in Python :
class Solution:
def solve(self, message):
if not message:
return 0
dp = [0 for x in range(len(message) + 1)]
dp[0] = 1
dp[1] = 0 if message[0] == "0" else 1
for i in range(2, len(message) + 1):
if 0 < int(message[i - 1 : i]) <= 9:
dp[i] += dp[i - 1]
if 10 <= int(message[i - 2 : i]) <= 26:
dp[i] += dp[i - 2]
return dp[len(message)]
```

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