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Problem20.java

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import java.util.*;

class Problem20 {

public static void main(String[] args) {

System.out.println(new Problem20().isValid("{}[(])"));

}

public boolean isValid(String s) {

if (s.length() <= 0) return true;

Stack<Character> stack = new Stack<>();

int i = 0;

char cur = s.charAt(i);

while(( cur = s.charAt(i) )!= '\0') {

switch (cur) {

case ']':

if (stack.isEmpty()) return false;

char c = stack.pop();

if (c != '[') return false;

break;

case '}':

if (stack.isEmpty()) return false;

c = stack.pop();

if (c != '{') return false;

break;

case ')':

if (stack.isEmpty()) return false;

c = stack.pop();

if (c != '(') return false;

break;

default:

stack.push(cur);

}

++i;

if (i == s.length()) {

break;

}

}

if (stack.isEmpty()) {

return true;

}

return false;

}

}