Identify the Approach

Question 1

Validate Parentheses
You are given a string s consisting of the following characters: ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[’ and ‘]’.

The input string s is valid if and only if:

Every open bracket is closed by the same type of close bracket.
Open brackets are closed in the correct order.
Every close bracket has a corresponding open bracket of the same type.
Return true if s is a valid string, and false otherwise.

Answer 1

1. Append all open bracket to a stack.
2. When a closing bracket is there check for matching bracket.
3. If match pop open bracket from stack.
4. If the stack is empty it should return true.

Question 2

Generate Parentheses
You are given an integer n. Return all well-formed parentheses strings that you can generate with n pairs of parentheses.

Example 1:

Input: n = 1

Output: [”()”]
Example 2:

Input: n = 3

Output: [”((()))”,”(()())”,”(())()”,”()(())”,”()()()”]
You may return the answer in any order.

Answer 2

1. Only add a open < n
2. only add a close < open
3. Valid If open == close == n
4. Use Recursion to backtrack .