#yyds干货盘点# leetcode-栈-20

数据结构-栈，先进后出，匹配括号时，可以将左括号放到栈中，如果遇到合适的右括号就出栈，最后如果栈是空的就代表成功

import java.util.ArrayList;
import java.util.Stack;

/**
<p>给定一个只包括 <code>'('</code>，<code>')'</code>，<code>'{'</code>，<code>'}'</code>，<code>'['</code>，<code>']'</code> 的字符串 <code>s</code> ，判断字符串是否有效。</p>

<p>有效字符串需满足：</p>

<ol>
    <li>左括号必须用相同类型的右括号闭合。</li>
    <li>左括号必须以正确的顺序闭合。</li>
</ol>

<p> </p>

<p><strong>示例 1：</strong></p>

<pre>
<strong>输入：</strong>s = "()"
<strong>输出：</strong>true
</pre>

<p><strong>示例 2：</strong></p>

<pre>
<strong>输入：</strong>s = "()[]{}"
<strong>输出：</strong>true
</pre>

<p><strong>示例 3：</strong></p>

<pre>
<strong>输入：</strong>s = "(]"
<strong>输出：</strong>false
</pre>

<p><strong>示例 4：</strong></p>

<pre>
<strong>输入：</strong>s = "([)]"
<strong>输出：</strong>false
</pre>

<p><strong>示例 5：</strong></p>

<pre>
<strong>输入：</strong>s = "{[]}"
<strong>输出：</strong>true</pre>

<p> </p>

<p><strong>提示：</strong></p>

<ul>
    <li><code>1 <= s.length <= 10<sup>4</sup></code></li>
    <li><code>s</code> 仅由括号 <code>'()[]{}'</code> 组成</li>
</ul>
<div><div>Related Topics</div><div><li>栈</li><li>字符串</li></div></div><br><div><li>👍 3187</li><li>👎 0</li></div>
*/

//leetcode submit region begin(Prohibit modification and deletion)
class Solution {
    public boolean isValid(String s) {
        Stack<Character> stack = new Stack<>();
        for (int i = 0; i < s.length(); i++) {
            Character c = s.charAt(i);
            if(c=='{'||c=='('||c=='['){
                stack.push(c);
            }else{
                if(stack.isEmpty()){
                    return false;
                }

                if(!stack.isEmpty()){
                    if(stack.peek()=='{' && c=='}'){
                        stack.pop();
                    }else if(stack.peek()=='[' && c==']'){
                        stack.pop();
                    }else if(stack.peek()=='(' && c==')'){
                        stack.pop();
                    }else{
                        return false;
                    }
                }
            }
        }
        return stack.isEmpty();
    }

}
//leetcode submit region end(Prohibit modification and deletion)