[JAVA/LeetCode] Top 100 Liked Question: 20. Valid Parentheses

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/**
 *
 * @author HEESOO
 *
 */
class Solution {
    public boolean isValid(String s) {
        Stack<Character> st=new Stack<>();
        
        for(int i=0;i<s.length();i++){
            char ch=s.charAt(i);
            if(ch=='(' || ch=='{' || ch=='[') st.push(ch);
            else{
                if(st.isEmpty()) return false;
                if(ch==')' && st.pop()!='(') return false;
                else if(ch=='}' && st.pop()!='{') return false;
                else if(ch==']' && st.pop()!='[') return false;
            }            
        }
        
        if(!st.isEmpty()) return false;
        
        return true;
    }
    
}