feat: solved 5

Author: fghpdf

src/com/fghpdf/LongestPalindromicSubstring/Solution.java

@@ -0,0 +1,80 @@
+package com.fghpdf.LongestPalindromicSubstring;
+
+/**
+ * @author fghpdf
+ * @date 2019/11/9
+ * https://leetcode.com/problems/longest-palindromic-substring/
+ * my way is slow
+ * discuss has a way to extend to search
+ *
+ **/
+public class Solution {
+	public String longestPalindrome(String s) {
+		if (s.length() == 0) {
+			return s;
+		}
+
+		int max = 0;
+		String result = "";
+		for (int i = s.length() - 1; i >= 0; i--) {
+			for (int j = 0; j < s.length();j++) {
+				if (i - j + 1 <= max) {
+					continue;
+				}
+				String sub = s.substring(j, i + 1);
+				if (isPalindrome(sub)) {
+					max = sub.length();
+					result = sub;
+				}
+			}
+		}
+		return result;
+	}
+
+	private boolean isPalindrome(String s) {
+		char[] chars = s.toCharArray();
+
+		for (int i = 0, j = chars.length - 1; i < j;) {
+			if (Character.toLowerCase(chars[i++]) != Character.toLowerCase(chars[j--])) {
+				return false;
+			}
+		}
+
+		return true;
+	}
+
+	private int lo, maxLen;
+
+	private String lo2(String s) {
+		int len = s.length();
+		if (len < 2) {
+			return s;
+		}
+
+		for (int i = 0; i < len-1; i++) {
+			extendPalindrome(s, i, i);  //assume odd length, try to extend Palindrome as possible
+			extendPalindrome(s, i, i+1); //assume even length.
+		}
+		return s.substring(lo, lo + maxLen);
+	}
+
+	private void extendPalindrome(String s, int j, int k) {
+		System.out.printf("%d %d\n", j, k);
+		while (j >= 0 && k < s.length() && s.charAt(j) == s.charAt(k)) {
+			j--;
+			k++;
+		}
+		System.out.printf("%d-%d\n", j, k);
+		if (maxLen < k - j - 1) {
+			lo = j + 1;
+			maxLen = k - j - 1;
+		}
+	}
+
+
+
+	public static void main(String[] args) {
+		Solution sol = new Solution();
+		System.out.println(sol.lo2("cbbd"));
+	}
+}