Kth Largest Element in an Array

Kth Largest Element in an Array

Total Accepted: 32668 Total Submissions: 109273 Difficulty: Medium

Find the kth largest element in an unsorted array. Note that it is the kth largest element in the sorted order, not the kth distinct element.

For example,
Given [3,2,1,5,6,4] and k = 2, return 5.

Note: 
You may assume k is always valid, 1 ≤ k ≤ array's length.

class Solution {
private:
    int partion(vector<int>& nums,int start,int end){
    
        if(end-start==1){
            return start;
        }
    
        srand(time(0));
        int rindex = start + rand()%(end-start);
        swap(nums[rindex],nums[end-1]);
        
        int i=start-1,j=start;
        while(j < end-1){
            if(nums[j] < nums[end-1]){
                swap(nums[++i],nums[j]);
            }
            ++j;
        }
        
        swap(nums[++i],nums[end-1]);
        
        return i;
    }
public:
    int findKthLargest(vector<int>& nums, int k) {
        int start = 0;
        int end   = nums.size();
        
        k = end - k;
        
        int index = partion(nums,start,end);
        while(index != k){
            if(index < k){
                start = index+1;
            }else{
                end = index;
            }
            index = partion(nums,start,end);
        }
        return nums.size()==0 ? 0 : nums[k];
    }
};