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]!='\0'
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
#includeint longest(char str[], int n){ int length = 0, i = n/2; if( n < 2 ) return 1; while( str[i]!='\0' ){ //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
