fd

Author: dingjikerbo

solution/src/main/java/com/inuker/solution/ShortestPalindrome.java

@@ -9,30 +9,16 @@
  */
 public class ShortestPalindrome {
     /**
-     * 其实只要将s与s的逆序串拼接在一起，求最长公共子串，逆序串中刨除这个最长公共子串，就是要加到s前面的
+     * 其实只要将s与s的逆序串拼接在一起，求最长公共子串
+     * 逆序串中从末尾刨除这个最长公共子串，就是要加到s前面的部分
+     * 比如对abcd，其逆序为dcba，拼接为abcddcba，最长公共子串为a，因此dcba刨除a后为dcb，即为要加到abcd前面的部分
      */
     public String shortestPalindrome(String s) {
         StringBuilder builder = new StringBuilder(s);
         return builder.reverse().substring(0, s.length() - getCommonLength(s)) + s;
     }
 
     private int getCommonLength(String str) {
-        StringBuilder builder = new StringBuilder(str);
-        String rev = new StringBuilder(str).reverse().toString();
-        builder.append("#").append(rev);
-        int[] p = new int[builder.length()];
-        for (int i = 1; i < p.length; i++) {
-            int j = p[i - 1];
-            while (j > 0 && builder.charAt(i) != builder.charAt(j)) j = p[j - 1];
-            p[i] = j == 0 ? (builder.charAt(i) == builder.charAt(0) ? 1 : 0) : j + 1;
-        }
-        return p[p.length - 1];
-    }
-
-    /**
-     * 更直观的写法
-     */
-    private int getCommonLength2(String str) {
         String rev = new StringBuilder(str).reverse().toString();
         return getCommonLength(str + rev, str.length());
     }

solution/src/main/java/com/inuker/solution/StrStr.java

@@ -7,6 +7,7 @@
 public class StrStr {
 
     // 这里非常重要的是i<=len1-len2，如果没有这个会超时
+    // 比如needle非常长的时候
     public int strStr(String haystack, String needle) {
         int l1 = haystack.length(), l2 = needle.length();
         for (int i = 0, j; i + l2 - 1 < l1; i++) {

test/src/main/java/com/inuker/test/main.java

@@ -28,27 +28,6 @@
 public class main {
 
     public static void main(String[] args) {
-        System.out.println(multiply("99", "100"));
     }
 
-    public static String multiply(String num1, String num2) {
-        int l1 = num1.length(), l2 = num2.length();
-        int[] result = new int[l1 + l2];
-        for (int i = l1 - 1; i >= 0; i--) {
-            for (int j = l2 - 1; j >= 0; j--) {
-                int n1 = num1.charAt(i) - '0';
-                int n2 = num2.charAt(j) - '0';
-                int n = result[i + j + 1] + n1 * n2;
-                result[i + j + 1] = n % 10;
-                result[i + j] += n / 10;
-            }
-        }
-        StringBuilder sb = new StringBuilder();
-        for (int i = 0; i < result.length; i++) {
-            if (result[i] != 0 || sb.length() > 0) {
-                sb.append(result[i]);
-            }
-        }
-        return sb.length() == 0 ? "0" : sb.toString();
-    }
 }