Leetcode First-Unique-Character-In-a-String

2022-06-14 13:10

Algorithms:

#algorithm

Data structures:

#DS #string #array #hash_table

Difficulty:

#leetcode #coding_problems #difficulty_easy

Problem

Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1.

Examples

Example 1:

**Input:** s = "leetcode"
**Output:** 0

Example 2:

**Input:** s = "loveleetcode"
**Output:** 2

Example 3:

**Input:** s = "aabb"
**Output:** -1

Constraints

1 <= s.length <= 105
s consists of only lowercase English letters.

Thoughts

Really, really simple hash map problem. Shouldn't have taken so much time.

[!summary] Don't overlook simple problems! #tip

Solution

class Solution {
public:
  int firstUniqChar(string s) {
    // O(1) hashmap
    int umap[26] = {};

    int sSize = s.size();
    for (int i = 0; i < sSize; i++) {
        umap[s[i] - 'a']++;
    }

    for (int i = 0; i < sSize; i++) {
      if (umap[s[i] - 'a'] == 1) {
        return i;
      }
    }
    return -1;
  }
};

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