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The brute force approach involves iterating over each possible starting position of the needle in the haystack and checking if the substring from that position matches the needle.
Time Complexity: O((m-n+1)*n), where m is the length of haystack and n is the length of needle.
Space Complexity: O(1).
1function strStr(haystack, needle) {
2 let m = haystack.length;
3 let n = needle.length;
4 if (n === 0) return 0;
5 for (let i = 0; i <= m - n; i++) {
6 let j = 0;
7 for (; j < n; j++) {
8 if (haystack[i + j] !== needle[j])
9 break;
10 }
11 if (j === n) return i;
12 }
13 return -1;
14}
15
16console.log(strStr("sadbutsad", "sad")); // Output: 0This JavaScript solution examines each substring of the haystack to check for a match with the needle.
The KMP (Knuth-Morris-Pratt) algorithm is a more efficient string-searching algorithm. It preprocesses the needle to create a longest prefix-suffix (LPS) array, which is used to skip unnecessary comparisons while searching in the haystack.
Time Complexity: O(m + n), where m is the length of haystack and n is the length of needle.
Space Complexity: O(n), due to the LPS array.
This C solution uses the KMP algorithm, which preprocesses the needle to create an LPS array, reducing the number of comparisons required.