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
int strStr(string haystack, string needle)
int strStr(string haystack, string needle)
{
if(needle.size()==0&&haystack.size()!=0)
return 0;
else if(needle.size()!=0&&haystack.size()==0)
return -1;
else if(needle.size()==0&&haystack.size()==0)
return 0;
else
{
int changdu=haystack.size()-needle.size();
for(int i=0;i<=changdu;i++)
{
if(haystack.substr(i,needle.size())==needle)
return i;
}
return -1;
}
}
1、边界情况的判定。haystack为空?needle为空?haystack比needle长度小?
2、haystack.substr(x,y),x为起始点index,y为长度,注意不可以让x和y超过haystack的限制。
3、string的size不是int类型,估计为unsigned类型。比如haystack="",needle="a",当cout<<haystack.size()-needle.size()<<endl;的时候,得到的会是一堆乱码,这时候强制类型转换,cout<<int(haystack.size()-needle.size())<<endl;才会得到-1的结果,这点在//**那里体现出来了。笔者在第一次submit的时候也犯了这个错误。