ValidParentheses20.kt

package easy

import java.util.*

/**
 * Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

An input string is valid if:

Open brackets must be closed by the same type of brackets.
Open brackets must be closed in the correct order.


Example 1:

Input: s = "()"
Output: true
Example 2:

Input: s = "()[]{}"
Output: true
Example 3:

Input: s = "(]"
Output: false


Constraints:

1 <= s.length <= 104
s consists of parentheses only '()[]{}'.
 */

fun isValid(s: String): Boolean {
    val stack=Stack<Char>()
    s.forEach { char->
        if(char=='('||char=='{'||char=='[')
        {
              stack.push(char)
        }else
        {
            if(stack.isNotEmpty())
            {
                val peek=stack.peek()
                if((peek=='('&& char==')')||(peek=='{'&& char=='}')||(peek=='['&& char==']'))
                {
                    stack.pop()
                }else
                    stack.push(char)
            }else
            {
                stack.push(char)
            }
        }
    }
return stack.isEmpty()
}