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LeetCode20.有效的括号
2022-07-05 12:39:00 【厚积薄发ض】
有效的括号
-->20. 有效的括号
这个也是栈的应用经典问题
输入:s = "( )" 输出:true 输入:s = "( )[ ]{ }" 输出:true
输入:s = "( ]" 输出:false 输入:s = "( [ ) ]" 输出:false
输入:s = "{ [ ] }" 输出:true
这个题就是一共有三种括号【】{} ()然后这三个可以混合也可以不混合,看是否是匹配的?
思路:
左括号都入栈,然后看遍历的字符是否与其匹配,如果匹配将栈顶左括号弹出继续遍历,如果最后栈中还有元素,或者还有没遍历完的字符串但栈已经为空都是不匹配的
class Solution {
public boolean isValid(String s) {
//如果是左括号就入栈
Stack<Character> stack = new Stack<>();
for(int i =0;i<s.length();++i){
//如果是左括号就入栈
if(s.charAt(i)=='('||s.charAt(i)=='['
||s.charAt(i)=='{'){
stack.push(s.charAt(i));
}else {
//如果不是右括号那就要与栈顶元素进行比较
if(stack.empty()){
//如果栈为空,无法比较
return false;
}else {
//栈不为空看是否是匹配的情况
if((stack.peek()=='('&&s.charAt(i)==')')
||(stack.peek()=='{'&&s.charAt(i)=='}')||
(stack.peek()=='['&&s.charAt(i)==']')){
stack.pop();
}else {
//如果相等弹出栈顶元素
return false;
}
}
}
}
return stack.empty();
}
}
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