题目要求
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| 在子字符串中寻找目标字符串，并返回该字符串第一次出现时的下标
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思路一
在原字符串中中寻找目标字符串首字母的下标，并提取子字符串，若该字符串的开头等于目标字符串，则返回该下标
优点：速度相对较快
缺点：深度依赖api
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| public int strStr(String haystack, String needle) {
int haystackLength = haystack.length();
int needleLength = needle.length();
if(haystackLength<needleLength){
return -1;
}else if(needleLength==0){
return 0;
}
char start = needle.charAt(0);
int index = haystack.indexOf(start);
while(index!=-1){
if(index+needleLength>haystackLength){
index = -1;
break;
}
if(haystack.substring(index).startsWith(needle)){
break;
}
int tempIndex = haystack.substring(index+1).indexOf(start);
index = tempIndex==-1?-1:(tempIndex+index+1);
}
return index;
}
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思路二
提取当前下标的子字符串并判断开头是否相等，相等则返回该下标
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| public int strStr2(String haystack, String needle){
int index = 0;
for( ; index+needle.length()<=haystack.length() ; index++){
if(haystack.substring(index).startsWith(needle)){
return index;
}
}
if(index+needle.length()==haystack.length()){
index = -1;
}
return index;
}
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