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/**

* 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.

*/

public class KthLargestElementInAnArray215 {

public int findKthLargest(int[] nums, int k) {

Arrays.sort(nums);

return nums[nums.length - k];

}

/**

* https://discuss.leetcode.com/topic/14597/solution-explained

*/

public int findKthLargest2(int[] nums, int k) {

final PriorityQueue<Integer> pq = new PriorityQueue<>();

for(int val : nums) {

pq.offer(val);

if(pq.size() > k) {

pq.poll();

}

}

return pq.peek();

}

/**

* https://discuss.leetcode.com/topic/14597/solution-explained

*/

public int findKthLargest3(int[] nums, int k) {

k = nums.length - k;

int lo = 0;

int hi = nums.length - 1;

while (lo < hi) {

final int j = partition(nums, lo, hi);

if(j < k) {

lo = j + 1;

} else if (j > k) {

hi = j - 1;

} else {

break;

}

}

return nums[k];

}

private int partition(int[] a, int lo, int hi) {

int i = lo;

int j = hi + 1;

while(true) {

while(i < hi && less(a[++i], a[lo]));

while(j > lo && less(a[lo], a[--j]));

if(i >= j) {

break;

}

exch(a, i, j);

}

exch(a, lo, j);

return j;

}

private void exch(int[] a, int i, int j) {

final int tmp = a[i];

a[i] = a[j];

a[j] = tmp;

}

private boolean less(int v, int w) {

return v < w;

}

/**

* https://discuss.leetcode.com/topic/14597/solution-explained

*/

public int findKthLargest4(int[] nums, int k) {

shuffle(nums);

k = nums.length - k;

int lo = 0;

int hi = nums.length - 1;

while (lo < hi) {

final int j = partition(nums, lo, hi);

if(j < k) {

lo = j + 1;

} else if (j > k) {

hi = j - 1;

} else {

break;

}

}

return nums[k];

}

private void shuffle(int a[]) {

final Random random = new Random();

for(int ind = 1; ind < a.length; ind++) {

final int r = random.nextInt(ind + 1);

exch(a, ind, r);

}

}

public int findKthLargest5(int[] nums, int k) {

int min = Integer.MAX_VALUE;

int max = Integer.MIN_VALUE;

for (int n: nums) {

min = Math.min(min, n);

max = Math.max(max, n);

}

if (min == max) return min;

while (min < max) {

int mid = min + (max - min) / 2;

int c = count(nums, mid);

if (c >= k) {

min = mid + 1;

} else {

max = mid;

}

}

return min;

}

private int count(int[] nums, int mid) {

int res = 0;

for (int n: nums) {

if (n > mid) res++;

}

return res;

}

public int findKthLargest6(int[] nums, int k) {

int len = nums.length;

int lo = 0;

int hi = len - 1;

while (lo < hi) {

int p = partition2(nums, lo, hi);

if (p == (len - k)) return nums[p];

if (p > (len - k)) {

hi = p - 1;

} else {

lo = p + 1;

}

}

return nums[lo];

}

private int partition2(int[] nums, int lo, int hi) {

if (lo == hi) return lo;

int slow = lo+1;

int fast = lo+1;

while (fast <= hi) {

if (nums[fast] < nums[lo]) {

swap(nums, slow, fast);

slow++;

}

fast++;

}

swap(nums, lo, slow-1);

return slow-1;

}

private void swap(int[] nums, int i, int j) {

if (i == j) return ;

int temp = nums[i];

nums[i] = nums[j];

nums[j] = temp;

}

}