leetcode-棧=20

import java.util.ArrayList; import java.util.Stack; /** <p>給定一個只包括 <code>'('</code>,<code>')'</code>,<code>'{'</code>,<code>'}'</code>,<code>'['</code>,<code>']'</code> 的字符串 <code>s</code> ,判斷字符串是否有效。</p> <p>有效字符串需滿足:</p> <ol> <li>左括號必須用相同類型的右括號閉合。</li> <li>左括號必須以正確的順序閉合。</li> </ol> <p> </p> <p><strong>示例 1:</strong></p> <pre> <strong>輸入:</strong>s = "()" <strong>輸出:</strong>true </pre> <p><strong>示例 2:</strong></p> <pre> <strong>輸入:</strong>s = "()[]{}" <strong>輸出:</strong>true </pre> <p><strong>示例 3:</strong></p> <pre> <strong>輸入:</strong>s = "(]" <strong>輸出:</strong>false </pre> <p><strong>示例 4:</strong></p> <pre> <strong>輸入:</strong>s = "([)]" <strong>輸出:</strong>false </pre> <p><strong>示例 5:</strong></p> <pre> <strong>輸入:</strong>s = "{[]}" <strong>輸出:</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> 僅由括號 <code>'()[]{}'</code> 組成</li> </ul> <div><div>Related Topics</div><div><li>棧</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)
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