28. Implement strstr() implement strstr()

Implement strStr().

Realization  strStr()  function .

Given two strings needle and haystack, return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Here are two strings  haystack and needle , Please come in haystack Find in string needle The first place the string appears （ Subscript from 0 Start ）. If it doesn't exist , Then return to   -1 .

Clarification:

explain ：

What should we return when needle is an empty string? This is a great question to ask during an interview.

When  needle  When it's an empty string , What value should we return ？ This is a good question in an interview .

For the purpose of this problem, we will return 0 when needle is an empty string. This is consistent to C's strstr() and Java's indexOf().

For this question , When  needle  When it's an empty string, we should return 0 . This is related to C Linguistic  strstr()  as well as Java Of  indexOf()  The definition matches .

Example 1:

Input: haystack = "hello", needle = "ll"
Output: 2

Example 1：

Input ：haystack = "hello", needle = "ll"
Output ：2

Example 2:

Input: haystack = "aaaaa", needle = "bba"
Output: -1

Example 2：

Input ：haystack = "aaaaa", needle = "bba"
Output ：-1

Constraints:

1 <= haystack.length, needle.length <=
haystack and needle consist of only lowercase English characters.

Tips ：

1 <= haystack.length, needle.length <=
haystack and needle It only consists of lowercase English characters

 

C Language ：

int strStr(char * haystack, char * needle){
    int h=0,n=0;
    for(h=0;;h++)
    {
        if(haystack[h]=='\0')
            break;
    }
    for(n=0;;n++)
    {
        if(needle[n]=='\0')
            break;
    }
    for(int i=0;i+n<=h;i++)
    {
        bool flag=true;
        for(int j=0;j<n;j++)
        {
            if(haystack[i+j]!=needle[j])
            {
                flag=false;
                break;
            }
        }
        if(flag)
        {
            return i;
        }
    }
    return -1;

}

Execution results ：         adopt

Execution time ：0 ms, In all  C  Defeated in submission 100.00% Users of

Memory consumption ：5.6 MB, In all  C  Defeated in submission 42.55% Users of

Pass the test case ：75 / 75