# Find the Index of the First Occurrence in a String Leetcode Solution

## Index Of the first Occurrence Leetcode Problem :

Given two strings needle and haystack, return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

## Index Of First Occurrence Leetcode Solution :

### Constraints :

•
• 1 <= haystack.length, needle.length <= 104
• haystack and needle consist of only lowercase English characters.

### Example 1:

Output: 0

Explanation: “sad” occurs at index 0 and 6.

The first occurrence is at index 0, so we return 0.

### Example 2:

Input: haystack = “leetcode”, needle = “leeto”

Output: -1

Explanation: “leeto” did not occur in “leetcode”, so we return -1.

In the “3 sum” problem you are given an integer array `nums`, the goal is to find all  unique triplets within the array such that the sum of the elements in each triplet is equal to zero (i.e.,`nums[i] + nums[j] + nums[k] == 0`), and the indices i, j, and k are all distinct (i.e., `i != j, i != k, and j != k`).

Here are the key points for the given constraints and examples:

• Constraints:

• The length of the nums array is between 3 and 3000.
• The values in the nums array can range from -100,000 to 100,000.

Approach :

Two Pointer approach:

• Initialize 2 pointers i and j, store starting index of i in ind.
• While haystack[i] and needle[j] are equal increament the i and j both pointer.
• if j has traversed all the needle string, so return the starting index of i, where you started.
• else again intialize j with 0, to traverse the string needle again.
• Update the i pointer with ind + 1.
• Repeat the steps from 2, if didn’t get the ans in previous step.
• return -1, after checking all the possibilities, out of the loop.
• End.

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