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#include <unordered_map>



class Solution {

public:

    // std::unordered_map<int, int> m;   <<---- this one works

    int size;



    /**

     * @param s: a string,  encoded message

     * @return: an integer, the number of ways decoding

     */

    int numDecodings(string &s) {

        // write your code here

        size = s.length();

        if(!size) return 0;



        std::unordered_map<int, int> m;     <<---- this doesn't work

        decode(s, 0, m);

    }



    /**

     *  Time : O(n), Space: O(1)

     */

    int decode(string &s, int i, std::unordered_map<int, int>& m) {

        if (m.count(i)) { return m[i]; }

        if (s[i] == '0') return 0;

        if (size == 1) return 1;

        if (i >= size - 1) return 1;



        int ways = decode(s, i + 1, m);

        int prefix = (s[i] - '0') * 10 + (s[i + 1] - '0');

        if (prefix <= 26) {

            ways += decode(s, i + 2, m);

        }



        m[i] = ways;

        return ways;

    }

};

#include <unordered_map>



class Solution {

public:

    // std::unordered_map<int, int> m;   <<---- this one works

    int size;



    /**

     * @param s: a string,  encoded message

     * @return: an integer, the number of ways decoding

     */

    int numDecodings(string &s) {

        // write your code here

        size = s.length();

        if(!size) return 0;



        std::unordered_map<int, int> m;     <<---- this doesn't work

        decode(s, 0, m);

    }



    /**

     *  Time : O(n), Space: O(1)

     */

    int decode(string &s, int i, std::unordered_map<int, int>& m) {

        if (m.count(i)) { return m[i]; }

        if (s[i] == '0') return 0;

        if (size == 1) return 1;

        if (i >= size - 1) return 1;



        int ways = decode(s, i + 1, m);

        int prefix = (s[i] - '0') * 10 + (s[i + 1] - '0');

        if (prefix <= 26) {

            ways += decode(s, i + 2, m);

        }



        m[i] = ways;

        return ways;

    }

};

#include <unordered_map>



class Solution {

public:

    // std::unordered_map<int, int> m;   <<---- this one works

    int size;



    /**

     * @param s: a string,  encoded message

     * @return: an integer, the number of ways decoding

     */

    int numDecodings(string &s) {

        // write your code here

        size = s.length();

        if(!size) return 0;



        std::unordered_map<int, int> m;     <<---- this doesn't work

        decode(s, 0, m);

    }



    /**

     *  Time : O(n), Space: O(1)

     */

    int decode(string &s, int i, std::unordered_map<int, int>& m) {

        if (m.count(i)) { return m[i]; }

        if (s[i] == '0') return 0;

        if (size == 1) return 1;

        if (i >= size - 1) return 1;



        int ways = decode(s, i + 1, m);

        int prefix = (s[i] - '0') * 10 + (s[i + 1] - '0');

        if (prefix <= 26) {

            ways += decode(s, i + 2, m);

        }



        m[i] = ways;

        return ways;

    }

};

#include <unordered_map>



class Solution {

public:

    // std::unordered_map<int, int> m;   <<---- this one works

    int size;



    /**

     * @param s: a string,  encoded message

     * @return: an integer, the number of ways decoding

     */

    int numDecodings(string &s) {

        // write your code here

        size = s.length();

        if(!size) return 0;



        std::unordered_map<int, int> m;     <<---- this doesn't work

        decode(s, 0, m);

    }



    /**

     *  Time : O(n), Space: O(1)

     */

    int decode(string &s, int i, std::unordered_map<int, int>& m) {

        if (m.count(i)) { return m[i]; }

        if (s[i] == '0') return 0;

        if (size == 1) return 1;

        if (i >= size - 1) return 1;



        int ways = decode(s, i + 1, m);

        int prefix = (s[i] - '0') * 10 + (s[i + 1] - '0');

        if (prefix <= 26) {

            ways += decode(s, i + 2, m);

        }



        m[i] = ways;

        return ways;

    }

};

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