Create string `a` out of substrings of string `b`. Return the minimum number of copies that you need to do this.\n\n**Example 1:**\n```\nInput: a="zaza", b="baz"\nOutput: 3\nExplanation:\ncopy1="z"\ncopy2="az"\ncopy3="a\na=copy1+copy2+copy3\n```\n\nhttps://leetcode.com/problems/shortest-way-to-form-string (premium)

Create string a out of substrings of string b. Return the minimum number of copies that you need to do this.\n\nExample 1:\n\nInput: a="zaza", b="baz"\nOutput: 