LeetCode, leetcodeoj

LeetCode, leetcodeoj
Description:
Implement strStr ().


Returns the index of the first occurrence of needle in haystack, or-1 if needle is not part of haystack.


It is actually a function to find the starting position of the substring.




Ideas:
This article uses a traditional solution, which involves two-layer traversal. For the character string haystack, move it one by one to determine whether the value of haystack [I... needle. Length] is equal to the value of needle.


The faster algorithm is KMP. The two articles are very clear:
Http://blog.csdn.net/v_july_v/article/details/7041827
Http://www.ruanyifeng.com/blog/2013/05/Knuth-Morris-Pratt_algorithm.html




Implementation Code:

public class Solution {    public int StrStr(string haystack, string needle) {        var i = 0;        while(i < haystack.Length - needle.Length + 1){            var k = i;            while(k < haystack.Length - needle.Length + 1){var s = haystack.Substring(k, needle.Length);                if(s == needle){                    return k;                }k++;            }i++;        }        return -1;    }}

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