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[LeetCode 28] Implement strStr()

Problem

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:

Input: haystack = "hello", needle = "ll"
Output: 2

Example 2:

Input: haystack = "aaaaa", needle = "bba"
Output: -1

Example 3:

Input: haystack = "", needle = ""
Output: 0

Constraints:

- 0 <= haystack.length, needle.length <= 5 * 104
- haystack and needle consist of only lower-case English characters.

Thoughts

  • We can find the first character in haystack that is the same as the first one in needle, then checking if the following characters are the same

Typescript

function strStr(haystack: string, needle: string): number {
    if(needle.length === 0) return 0;
    
    let res = -1;
    
    for(let i = 0; i < haystack.length; i++){
        if(res !== -1) break;
        // we can check needle here
        if(haystack[i] === needle[0]) {
            let temp = true
            // check next few characters in haystack with needle
            for(let j = i + 1; j < needle.length + i; j++) {
                if(haystack[j] !== needle[j - i]) {
                    temp = false;
                }
            }
            if(temp) {
                res = i;
                return res;
            }
        }
    }
    
    return res;
};

Reference