</>Ali · LeetCode
#0028·EasyStrings

Find the Index of the First Occurrence in a String

LeetCode #28 · Easy · Strings · C++ solution with worked-out approach and complexity analysis.

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Approach

Use built-in string find function

The find() function returns the position of the first occurrence, or string::npos if not found.

Time
O(n*m)
worst case
Space
O(1)
Problem description(from LeetCode)

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.

Examples

Example 1
Input:
haystack = "sadbutsad", needle = "sad"
Output:
0

Constraints

  • •1 <= haystack.length, needle.length <= 10^4
  • •haystack and needle consist of only lowercase English characters.

C++ Solution

solution.cpp
class Solution {
public:
int strStr(string haystack, string needle) {
    auto ind = haystack.find(needle);
    return ind != string::npos ? int(ind) : -1;
  }
};

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