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package Algorithms.stack;

import java.util.Stack;

public class IsValid {

public boolean isValid1(String s) {

if (s == null || s.length() == 0) {

return true;

}

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

int len = s.length();

for (int i = 0; i < len; i++) {

char c = s.charAt(i);

if (stack.isEmpty()) {

if (c == ']' || c == ')' || c == '}') {

return false;

}

stack.push(c);

continue;

}

if (c == ')' && stack.peek() == '('

|| c == ']' && stack.peek() == '['

|| c == '}' && stack.peek() == '{'

) {

stack.pop();

} else if (c == '(' || c == '[' || c == '{') {

stack.push(c);

} else {

return false;

}

}

return stack.isEmpty();

}

public boolean isValid(String s) {

if (s == null) {

return false;

}

int len = s.length();

// bug 1: don't use s as the name of the stack.

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

for (int i = 0; i < len; i++) {

char c = s.charAt(i);

switch(c) {

case '(':

case '[':

case '{':

stk.push(c);

break;

case ')':

if (!stk.isEmpty() && stk.peek() == '(') {

stk.pop();

} else {

return false;

}

break;

case '}':

if (!stk.isEmpty() && stk.peek() == '{') {

stk.pop();

} else {

return false;

}

break;

case ']':

if (!stk.isEmpty() && stk.peek() == '[') {

stk.pop();

} else {

return false;

}

break;

}

}

return stk.isEmpty();

}

}