2707-extra-characters-in-a-string.cpp

/*
  You are given a 0-indexed string s and a dictionary of words dictionary. 
  You have to break s into one or more non-overlapping substrings such that each substring is present in dictionary. 
  There may be some extra characters in s which are not present in any of the substrings.

  Return the minimum number of extra characters left over if you break up s optimally.

  Ex. Input: s = "leetscode", dictionary = ["leet","code","leetcode"]
      Output: 1
      Explanation: We can break s in two substrings: "leet" from index 0 to 3 and "code" from index 5 to 8. There is only 1 unused character (at index 4), so we return 1.

  Time  : O(N^M)    M = dictionary.size(), N = s.size()
  Space : O(N)
*/

class Solution {
public:
    int minExtraChar(string s, vector<string>& dictionary) {
        int n = s.size();
        vector<int> dp(n + 1, n);

        dp[0] = 0; 

        for (int i = 1; i <= n; ++i) {
            for(int j = 0 ; j < dictionary.size() ; ++j) {
                int len = dictionary[j].size();
                if (i >= len && s.substr(i - len, len) == dictionary[j]) {
                    dp[i] = min(dp[i], dp[i - len]);
                }
            }
            dp[i] = min(dp[i], dp[i - 1] + 1);
        }

        return dp[n];
    }
};