20. Valid Parentheses

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LeetCode

Approach: Stacks

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class Solution {
    public boolean isValid(String s) {
        LinkedList<Character> ans=new LinkedList<>();
        
        for(int i=0;i<s.length();i++){
           if(ans.size()>0&&is_pairs(ans.peek(), s.charAt(i))){
               ans.pop();
           }else{
                ans.push(s.charAt(i));
           } 
        }
        return ans.isEmpty();
    }
    
    public boolean is_pairs(char a, char b){
        if(a=='('&&b==')') return true;
        if(a=='{'&&b=='}') return true;
        if(a=='['&&b==']') return true;
        return false;
    }
}

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