LeetCode-28. Implement strStr()

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本文深入解析了KMP算法在字符串匹配中的应用，通过一个具体的C++实现案例，展示了如何高效地寻找一个字符串在另一个字符串中首次出现的位置。特别讨论了当目标字符串为空时的特殊情况处理。

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Implement strStr().

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

Example 1:

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

Example 2:

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

Clarification:

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

这道题目显然是要考虑使用KMP算法的，那么现在就来写一个比较简单的KMP算法。

class Solution {
public:
int strStr(string haystack, string needle) {
int m = haystack.length(), n = needle.length();
if (!n) {//如果子字符串为空
return 0;
}
//kmp
for (int i = 0; i < m - n + 1; i++) {
int j = 0;
for (; j < n; j++) {
if (haystack[i + j] != needle[j]) {
break;
}
}
if (j == n) {
return i;
}
}
return -1;
}
};