28. 實現(xiàn) strStr() - 力扣（LeetCode） (leetcode-cn.com)

class?Solution?{

????public?int?strStr(String?haystack,?String?needle)?{

????????/**

?????????*?如果needle長度為0，返回0

?????????*?循環(huán)體分別使用i,j指向兩個字符串開始位置，循環(huán)條件i<haystack.length?&&?j<needle.length()

?????????*?????如果haystack.charAt(i)==needle.charAt(j)?i++,j++?用res?=?i更新位置

?????????*?????如果haystack.charAt(i)!=needle.charAt(j)?i++

?????????*?退出循環(huán)時，如果j==needle.length()，則開始位置為

?????????*?j<=needle的長度，返回-1

?????????*?*/

????????if(needle.length()<1)?return?0;

????????int?i=0,j=0,res=0;

????????while(i<haystack.length()&&j<needle.length())?{

????????????if?(haystack.charAt(i)?==?needle.charAt(j)){

????????????????j++;

????????????}

????????????j?=?0;

????????????i++;

????????}

????????if(j==needle.length())?res?=?i-j;

????????else?res?=?-1;

????????return?res;

????}

}