5:最长回文子串

src/main/java/leetcode/editor/cn/LongestPalindromicSubstring.java

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+//给你一个字符串 s，找到 s 中最长的回文子串。 
+//
+// 
+//
+// 示例 1： 
+//
+// 
+//输入：s = "babad"
+//输出："bab"
+//解释："aba" 同样是符合题意的答案。
+// 
+//
+// 示例 2： 
+//
+// 
+//输入：s = "cbbd"
+//输出："bb"
+// 
+//
+// 示例 3： 
+//
+// 
+//输入：s = "a"
+//输出："a"
+// 
+//
+// 示例 4： 
+//
+// 
+//输入：s = "ac"
+//输出："a"
+// 
+//
+// 
+//
+// 提示： 
+//
+// 
+// 1 <= s.length <= 1000 
+// s 仅由数字和英文字母（大写和/或小写）组成 
+// 
+// Related Topics 字符串 动态规划 
+// 👍 3593 👎 0
+
+package leetcode.editor.cn;
+
+import java.util.Collections;
+
+//5:最长回文子串
+public class LongestPalindromicSubstring {
+    public static void main(String[] args) {
+        //测试代码
+        Solution solution = new LongestPalindromicSubstring().new Solution();
+        //bab
+        System.out.println(solution.longestPalindrome("babad"));
+        //bb
+        System.out.println(solution.longestPalindrome("cbbd"));
+        //a
+        System.out.println(solution.longestPalindrome("a"));
+        //a
+        System.out.println(solution.longestPalindrome("ac"));
+        //ccc
+        System.out.println(solution.longestPalindrome("ccc"));
+    }
+
+    //力扣代码
+    //leetcode submit region begin(Prohibit modification and deletion)
+    class Solution {
+        public String longestPalindrome(String s) {
+            int length = s.length();
+            if (length < 2) {
+                return s;
+            }
+            boolean[][] bl = new boolean[length][length];
+            for (int i = 0; i < length; i++) {
+                bl[i][i] = true;
+            }
+            int index = 0;
+            int max = 1;
+            for (int i = 2; i <= length; i++) {
+                for (int start = 0; start < length && i + start - 1 < length; start++) {
+                    int end = i + start - 1;
+                    if (s.charAt(start) != s.charAt(end)) {
+                        bl[start][end] = false;
+                    } else {
+                        if (i <= 3) {
+                            bl[start][end] = true;
+                        } else {
+                            bl[start][end] = bl[start + 1][end - 1];
+                        }
+                    }
+
+                    if (bl[start][end] && i > max) {
+                        max = i;
+                        index = start;
+                    }
+                }
+            }
+            return s.substring(index, index + max);
+        }
+    }
+//leetcode submit region end(Prohibit modification and deletion)
+
+}

src/main/java/leetcode/editor/cn/LongestPalindromicSubstring.md

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+<p>给你一个字符串 <code>s</code>，找到 <code>s</code> 中最长的回文子串。</p>
+
+<p> </p>
+
+<p><strong>示例 1：</strong></p>
+
+<pre>
+<strong>输入：</strong>s = "babad"
+<strong>输出：</strong>"bab"
+<strong>解释：</strong>"aba" 同样是符合题意的答案。
+</pre>
+
+<p><strong>示例 2：</strong></p>
+
+<pre>
+<strong>输入：</strong>s = "cbbd"
+<strong>输出：</strong>"bb"
+</pre>
+
+<p><strong>示例 3：</strong></p>
+
+<pre>
+<strong>输入：</strong>s = "a"
+<strong>输出：</strong>"a"
+</pre>
+
+<p><strong>示例 4：</strong></p>
+
+<pre>
+<strong>输入：</strong>s = "ac"
+<strong>输出：</strong>"a"
+</pre>
+
+<p> </p>
+
+<p><strong>提示：</strong></p>
+
+<ul>
+	<li><code>1 <= s.length <= 1000</code></li>
+	<li><code>s</code> 仅由数字和英文字母（大写和/或小写）组成</li>
+</ul>
+<div><div>Related Topics</div><div><li>字符串</li><li>动态规划</li></div></div>\n<div><li>👍 3593</li><li>👎 0</li></div>