[leetcode][string] Implement strStr()

题目：

Implement strStr().

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

Update (2014-11-02):

The signature of the function had been updated to return the index instead of the pointer. If you still see your function signature returns a

char
*

or

String

, please click the reload button to
reset your code definition.

class Solution {
public://KMP
int strStr(string haystack, string needle) {
if(needle.empty()) return 0;
if(haystack.empty()) return -1;
//    int *next = new int[needle.size()];
int next[needle.size()];
getNext(needle, next);
int i = 0, j = 0;
int lenHaystack = haystack.size();
int lenNeedle = needle.size();
while(i < lenHaystack && j < lenNeedle){
if(j == -1 || haystack[i] == needle[j]){
++j;
++i;
}
else j = next[j];//不匹配额时候不不移动i指针
}
//     delete []next;
return j == needle.size() ? i - j : -1;
}
private:
void getNext(string needle, int *next){
next[0] = -1;
int i = 0, j = -1;
while(i < needle.size()){
if(j == -1 || needle[i] == needle[j]){
++i;
++j;
next[i] = j;
}
else{//不匹配额时候不不移动i指针
j = next[j];
}
}
}
};

遇到了两个很诡异的问题：

1.在leetcode中，用new动态分配数组会出现Runtime Error，而用变量（！！！）表示数组长度直接分配空间。不懂不懂。。。。。。

2.在vs2013中，可以new数组，但是delete []next时程序就跑飞了，在调用getNext之前delete就没问题，难道vs在编译时做了什么优化?不懂不懂。。。。。。

谁能告诉我这是什么鬼。。。。。。