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IsValid.java
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IsValid.java
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import java.util.*;
public class IsValid {
public boolean isValid(String s) {
if (s == null){
return false;
}
int n = s.length();
if (n % 2 == 1) {
return false;
}
// char[] s1 = s.toCharArray();
// char[] s2 = s.toCharArray();
// Stack<Character> stack = new Stack<Character>();
// Queue<Character> queue = new LinkedList<Character>();
Map<Character, Character> pairs = new HashMap<>() {{
put(')', '(');
put(']', '[');
put('}', '{');
}};
// 左括号 入栈 右括号 出栈 peek不等于 value 返回 false 栈为空返回true
Deque<Character> stack = new LinkedList<Character>();
for (int i = 0; i < n; i++) {
char ch = s.charAt(i);
if (pairs.containsKey(ch)) {
if (stack.isEmpty() || stack.peek() != pairs.get(ch)) {
return false;
}
stack.pop();
} else {
stack.push(ch);
}
}
return stack.isEmpty();
}
}