String的细节

It comes from a problem from LeetCode Portal

String s 

i use the clause that s[i] to get the ith letter in string s. Surely, it's wrong.

Because the expression of s[i]  means that the s is an array. However, it's a string.

we can use the below function.

• s.charAt(int index)
• char[] arr = s.toCharArray()