leetcode KthlargestNumber
z
 2019-04-09 10:36:27   
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public class KthlargestNumber {
  /**
   * 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.
   *
   * Example 1:
   *
   * Input: [3,2,1,5,6,4] and k = 2
   * Output: 5
   * Example 2:
   *
   * Input: [3,2,3,1,2,4,5,5,6] and k = 4
   * Output: 4
   * Note:
   * You may assume k is always valid, 1 ≤ k ≤ array's length.
   */
  public static int findKthLargest(int[] nums, int k) {
    int left = 0;
    int right = nums.length-1;
    while(true){
      if (left == right){
        return nums[right];
      }
      int pivotIndex = left + (right - left)/2;
      pivotIndex = partition(nums, left, right, pivotIndex);
      if (pivotIndex == k ){
        return nums[pivotIndex];
      }
      else if (pivotIndex > k){
        right = pivotIndex - 1;
      }
      else
        left = pivotIndex + 1;

    }
  }

  public static int partition(int[] nums, int left, int right, int pivotIndex){
    int index = left;
    int pivotValue = nums[pivotIndex];
    swap(nums, right, pivotIndex);
    for (int i=left; i< right; i++){
      if (nums[i] > pivotValue){
        swap(nums, i, index);
      }
      index ++;
    }
    swap(nums, index, right);
    return index;
  }

  // swap two values.
  public static void swap(int[] nums, int left, int right){
    int temp = nums[left];
    nums[left] = nums[right];
    nums[right] = temp;
  }
  public static void main(String[] args){

  }
}