https://leetcode.com/problems/shortest-way-to-form-string/description/

A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e., "ace" is a subsequence of "abcde" while "aec" is not).

Given two strings source and target, return the minimum number of subsequences of source such that their concatenation equals target. If the task is impossible, return -1.

Example 1:

Input: source = "abc", target = "abcbc"
Output: 2
Explanation: The target "abcbc" can be formed by "abc" and "bc", which are subsequences of source "abc".

Example 2:

Input: source = "abc", target = "acdbc"
Output: -1
Explanation: The target string cannot be constructed from the subsequences of source string due to the character "d" in target string.

Example 3:

Input: source = "xyz", target = "xzyxz"
Output: 3
Explanation: The target string can be constructed as follows "xz" + "y" + "xz".

Constraints:

• 1 <= source.length, target.length <= 1000
• source and target consist of lowercase English letters.

class Solution {
public:
    int shortestWay(string source, string target) {
        //explain subsequence. it is a special string that remain relative position in original string
        //we use sub of source and use them to form target
        //traverse target and for each target[i] try to find matched ch in source. so we need to traverse source.
            //traverse source
                //if find matched ch in source, then increase both string index and try to find next match ch
            //if in current loop, num of matched is 0, then return -1
            //otherwise i+=num of matched
        int loops=0;
        for(int i=0;i<target.size();){
            int matched=0;
            for(int j=0;j<source.size();j++){
                if(target[i+matched]==source[j]){
                    matched++;
                }
            }
            if(matched==0){
                return -1;
            }else{
                i+=matched;
                loops++;
            }
        }
        return loops;
    }
};

Beats 100% and only one submit no debug. It seems finally i grasp some trick? Amazing.