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stackParentheses.java
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stackParentheses.java
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import java.util.*;
public class stackParentheses {
//push opening bracket in stack
//for closing bracket, if top and it form a pair, pop. else return false.
//also check if stack is not empty and string is finished, then also we return false.
public static boolean isValid(String str){
Stack<Character> s = new Stack<>();
for(int i = 0; i<str.length();i++){
char ch = str.charAt(i);
//opening
if(ch == '(' || ch=='{' || ch=='['){
s.push(ch);
}else{
//closing
if(s.isEmpty()){
return false;
}
if((s.peek()=='(' && ch ==')')
|| (s.peek()=='{' && ch=='}')
|| (s.peek()=='[' && ch==']')){
s.pop();
}else{
return false;
}
}
}
if(s.isEmpty()){
return true;
}else{
return false;
}
}
public static boolean isDuplicate(String str){
Stack<Character> s = new Stack<>();
for(int i = 0; i<str.length(); i++){
char ch = str.charAt(i);
//closing
if(ch ==')'){
int count=0;
while(s.pop()!='('){
s.pop();
count++;
}
if(count<1){
return true;
}
}else{
//opening
s.push(ch);
}
}
return false;
}
public static void main(String[] args) {
// String str="{[()]}(";
// System.out.println(isValid(str));
String str = "(a+b)";
System.out.println(isDuplicate(str));
}
}
//time complexity = O(n)