Print out the longest part of a given string that is both a prefix and a suffix of the string, in a C program

给定一个字符串，我们必须检查最长前缀的长度，它也是字符串的后缀，就像有一个字符串“abcab”，所以这里“ab”的长度为2，是最长的子字符串相同的前缀和后缀。

示例

Input: str[] = { “aabbccdaabbcc” }
Output: 6
Input: abdab
Output: 2

如果我们从字符串的开头和结尾开始指针，那么它们会在某个点重叠，所以我们不会这样做，而是从中间断开字符串并开始匹配左右字符串。如果它们相等，则任何一个匹配字符串的返回大小相同，否则尝试两侧的长度较短。

算法

int longest(char str[], int n)
START
STEP 1 : DECLARE length AS 0 AND i AS n/2
STEP 2 : IF n < 2 THEN
   RETURN 1
STEP 3 :LOOP WHILE TILL str[i]!=&#39;\0&#39;
   IF str[i] == str[length] THEN,
      INCREMENT length BY 1
      INCREMENT i BY 1
   ELSE
      IF length == 0 THEN,
         INCREMENT i BY 1
      ELSE
         DECREMENT length BY 1
      END IF
   END IF
END WHILE
RETURN length
STOP

示例

#include <stdio.h>
int longest(char str[], int n){
   int length = 0, i = n/2;
   if( n < 2 )
      return 1;
   while( str[i]!=&#39;\0&#39; ){
      //When we find the character like prefix in suffix,
      //we will move the length and i to count the length of the similar prefix and suffix
      if (str[i] == str[length]){
         ++length;
         ++i;
      } else //When prefix and suffix not equal{
         if(length == 0)
            ++i;
         else
            --length;
      }
   }
   return length;
}
int main(int argc, char const *argv[]){
   char str[] = {"abccmmabcc"};
   int n = sizeof(str)/sizeof(str[0]);
   int length = longest(str, n);
   printf("Length = %d", length);
   return 0;
}

输出

如果我们运行上面的程序，它将生成以下输出：

Length = 4

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