Number of Matching Subsequences in C++

Suppose we have a string S and a dictionary of words words, find the number of words[i] that is a subsequence of S. So if the input is S= “abcde” and dictionary is [“a”, “bb”, “acd”, “ace”], then output will be 3. Because there are three sequence of words in the dictionary, that are a subsequence of S: “a” “acd” and “ace”

To solve this, we will follow these steps −

• n := size of words array
• create one map m
• for i in range 0 to size of words
  • insert words[i] into the map m[words[i, 0]] position
• ans := 0
• for i in range 0 to size of S
  • char x := S[i]
  • if x is present in the map m, then
    • temp := m[x], and delete m[x]
    • for j in range 0 to temp size
      • if size of temp[j] = 1, then increase ans by 1, otherwise insert substring of temp[j] from index 1 into m[temp[j, 1]]
• return ans

Let us see the following implementation to get better understanding −

Example

 Live Demo

#include <bits/stdc++.h>
using namespace std;
class Solution {
   public:
   int numMatchingSubseq(string S, vector<string>& words) {
      int n = words.size();
      map <char, vector <string> > m;
      for(int i = 0; i < words.size(); i++){
         m[words[i][0]].push_back(words[i]);
      }
      int ans = 0;
      for(int i = 0; i < S.size(); i++){
         char x = S[i];
         if(m.find(x) != m.end()){
            vector <string> temp = m[x];
            m.erase(x);
            for(int j = 0; j < temp.size(); j++){
               if(temp[j].size() == 1){
                  ans++;
               } else {
                  m[temp[j][1]].push_back(temp[j].substr(1));
               }
            }
         }
      }
      return ans;
   }
};
int main() {
   Solution ob1;
   string s = "abcde";
   vector<string> v{"a","bb","acd","ace"};
   cout << ob1.numMatchingSubseq(s, v) << endl;
   return 0;
}

Input

"abcde"
["a","bb","acd","ace"]
string s = "abcde";
vector<string> v{"a","bb","acd","ace"};

Output

3