DecodeMessage-LCQ.cpp

/*
Decode the Message

You are given the strings key and message, which represent a cipher key and a secret message, respectively. The steps to decode message are as follows:

- Use the first appearance of all 26 lowercase English letters in key as the order of the substitution table.
- Align the substitution table with the regular English alphabet.
- Each letter in message is then substituted using the table.
- Spaces ' ' are transformed to themselves.

For example, given key = "happy boy" (actual key would have at least one instance of each letter in the alphabet), we have the partial substitution table of ('h' -> 'a', 'a' -> 'b', 'p' -> 'c', 'y' -> 'd', 'b' -> 'e', 'o' -> 'f').
Return the decoded message.



Example 1:


Input: key = "the quick brown fox jumps over the lazy dog", message = "vkbs bs t suepuv"
Output: "this is a secret"
Explanation: The diagram above shows the substitution table.
It is obtained by taking the first appearance of each letter in "the quick brown fox jumps over the lazy dog".

Example 2:


Input: key = "eljuxhpwnyrdgtqkviszcfmabo", message = "zwx hnfx lqantp mnoeius ycgk vcnjrdb"
Output: "the five boxing wizards jump quickly"
Explanation: The diagram above shows the substitution table.
It is obtained by taking the first appearance of each letter in "eljuxhpwnyrdgtqkviszcfmabo".


Constraints:

26 <= key.length <= 2000
key consists of lowercase English letters and ' '.
key contains every letter in the English alphabet ('a' to 'z') at least once.
1 <= message.length <= 2000
message consists of lowercase English letters and ' '.
*/

class Solution {
public:
	string decodeMessage(string key, string message) {
		char alpha[] = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'};
		int idx = 0;
		string res;
		map<char, char>mp;
		for (char ch : key) {
			if (ch == ' ') continue;
			else if (mp.find(ch) != mp.end())  continue;
			else    mp[ch] = alpha[idx++];
		}
		for (char ch : message) {
			if (ch == ' ') res += ' ';
			else    res += mp[ch];
		}
		return res;
	}
};