# 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') dp = 1;
dp = 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 = 1
dp = 0 if message == "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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