> For the complete documentation index, see [llms.txt](https://maksimdan.gitbook.io/interview-practice-problems/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://maksimdan.gitbook.io/interview-practice-problems/coding_practice_questions/hard/majority-element.md).

# Majority Element

**17.10 Majority Element:** A majority element is an element that makes up more than half of the items in an array. Given a positive integers array, find the majority element. If there is no majority element, return -1. Do this in 0 (N) time and O( 1) space.

```
EXAMPLE
Input: 1 2 5 9 5 9 5 5 5
Output: 5
```

**Complexity**: O(n) time and O(1) space

**The Idea**: The majority element of an array is guareenteed to be iterated over `floor(n/2)` times. Less frequent elements are then filtered out because contrasting elements cancel each other out.

```cpp
int majorityElement(vector<int>& nums) {
    if (nums.empty()) return -1;

    int maj = nums[0];
    int count = 1;

    for (int i = 1; i < nums.size(); i++) {
        if (!count) {
            maj = nums[i];
            count++;
        }
        else if (nums[i] == maj) count++;
        else count--;

    }
    return maj;
}

int main()
{
    vector<int> t1 = { 1, 2, 5, 9, 5, 9, 5, 5, 5 };
    cout << majority_element(t1);
}
```


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