leetcode-栈=20

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)