0%

2020-01-17-ImplementStr

LeetCode28

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().

Solution

如果不考虑java偷懒的写法当然可以想到indexof的想法

1
2
3
4
5
6
class Solution {
public int strStr(String haystack, String needle) {
return haystack.indexOf(needle);
}
}
Runtime: 1 ms

先按照题意写了如下代码:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
class Solution {
public int strStr(String haystack, String needle) {
if(needle.length()==0)return 0;
if(haystack.length()==0)return -1;
int index =-1;
boolean flag = true;
for(int i=0;i<haystack.length();i++){
if(haystack.charAt(i)==needle.charAt(0)){
flag=true;
for(int j =0;j<needle.length();j++){
if(i+j>=haystack.length()){
return -1;
}
if(haystack.charAt(i+j)!=needle.charAt(j)){
flag=false;
break;
};
}
if(flag){
return i;
}
}

}
return index;
}
}
Runtime: 4 ms
Memory Usage: 42.7 MB