实现strStr

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().

 

Constraints:

haystack and needle consist only of lowercase English characters.

实现代码

实现的关键就是使用substring()方法，将整个字符串分成与目标字符串的长度相同的小段，然后使用equals方法比较，如果有相同的，则返回开始的角标

package easy;

class SolutionStr{
    public int strStr(String hystack,String needle){
        int len1 = hystack.length();
        int len2 = needle.length();
        if(len2 > len1){
            return -1;
        }
        if(len2 == 0){
            return 0;
        }
        for(int i = 0;i < len1 - len2 + 1; ++i){
            if(hystack.substring(i,i+len2).equals(needle)){
                return i;
            }
        }
        return -1;
    }
}
public class ImplstrStr {
    public static void main(String[] args) {
        SolutionStr solution = new SolutionStr();
        System.out.println(solution.strStr("leetcode","ee"));
    }
}