Min Heap Construction

• Space : O(n)

#include <vector>
using namespace std;

// Do not edit the class below except for the buildHeap,
// siftDown, siftUp, peek, remove, and insert methods.
// Feel free to add new properties and methods to the class.
class MinHeap {
public:
    vector<int> heap;

    MinHeap(vector<int> vector) { // O(n logn)
			buildHeap(vector); 
		}

    void buildHeap(vector<int> &vector) {
        for(auto& a : vector)
            insert(a);
    }

    void siftDown() { // O(logn)
        int i = 0;
        while(true) {
            int child1 = i * 2 + 1, child2 = i * 2 + 2;
            if(child1 >= heap.size()) return;
            if(child2 >= heap.size()) {
                if(heap[child1] < heap[i]) {
                    swap(heap[child1], heap[i]);
                    i = child1;
                } else return;
            } else {
                if(heap[child1] > heap[child2]) {
                    if(heap[child2] < heap[i]) {
                        swap(heap[child2], heap[i]);
                        i = child2;
                    } else return;
                } else {
                    if(heap[child1] < heap[i]) {
                        swap(heap[child1], heap[i]);
                        i = child1;
                    } else return;
                }
            }
        }
    }

    void siftUp() { // O(logn)
        int i = heap.size() - 1;
        while(i) {
            int par = (i - 1)/ 2;
            if(heap[par] > heap[i]) {
                swap(heap[par], heap[i]);
                i = par;
            } else return;
        }
    }

    int peek() { // O(1)
        if(heap.empty()) return -1;
        return heap[0];
    }

    int remove() { // O(logn)
        int res = heap[0];
        heap[0] = heap.back();
        heap.pop_back();
        siftDown();
        return res;
    }

    void insert(int value) { // O(logn)
        heap.push_back(value);
        siftUp();
    }
};