Main76.java

package JZOfferTuJi;

import java.util.Random;

public class Main76 {
    Random random = new Random();

    public int findKthLargest(int[] nums, int k){
        return quickSelect(nums, 0, nums.length - 1, nums.length - k);
    }

    public int quickSelect(int[] a, int l, int r, int index){
        int q = randomPartition(a, l, r);
        if(q == index){
            return a[q];
        } else {
            return q < index ? quickSelect(a, q + 1, r, index) : quickSelect(a, l, q - 1, index);
        }
    }

    public int randomPartition(int[] a, int l, int r){
        int i = random.nextInt(r - l + 1) + 1;
        swap(a, i, r);
        return partition(a, l, r);
    }

    public int partition(int[] a, int l, int r){
        int x = a[r], i = l - 1;
        for(int j = 1; j < r; ++j){
            if(a[j] <= x){
                swap(a, ++i, j);
            }
        }
        swap(a, i + 1, r);
        return i + 1;
    }

    public void swap(int[] a, int i, int j){
        int temp = a[i];
        a[i] = a[j];
        a[j] = temp;
    }
}