Implement strStr() Problem
Description
LeetCode Problem 28.
Implement strStr().
Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
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().
Example 1:
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Input: haystack = "hello", needle = "ll"
Output: 2
Example 2:
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Input: haystack = "aaaaa", needle = "bba"
Output: -1
Example 3:
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Input: haystack = "", needle = ""
Output: 0
Constraints:
- 0 <= haystack.length, needle.length <= 5 * 10^4
- haystack and needle consist of only lower-case English characters.
Sample C++ Code
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class Solution {
public:
int strStr(string haystack, string needle) {
int l1 = haystack.size(), l2 = needle.size();
int i = 0, j = 0, k = 0;
if (l2 == 0)
return 0;
if (l1 == 0)
return -1;
bool isSub = true;
while (i < l1 - l2 + 1) {
if (haystack[i] == needle[0]) {
isSub = true;
for (k = 0; k < l2; k ++) {
if (haystack[i + k] != needle[k]) {
isSub = false;
break;
}
}
if (isSub)
return i;
}
i ++;
}
return -1;
}
};