LintCode刷题5

描述

在数组中找到第 k 大的元素。

你可以交换数组中的元素的位置

样例

样例 1：

输入：
n = 1, nums = [1,3,4,2]
输出：
4

样例 2：

输入：
n = 3, nums = [9,3,2,4,8]
输出：
4

挑战

要求时间复杂度为O(n)，空间复杂度为O(1)。

可以使用快排/堆排等等，这里我使用选择排序。

public class Exp5 {
    public static int findMax(int n, int[] nums){
        // write your code here
        int result = nums[0];
        for (int i = 0; i < nums.length; i++) {
            int max = nums[i];
            int max_index = i;
            for (int j = i; j < nums.length; j++) {
                if (max < nums[j]) {
                    max = nums[j];
                    max_index = j;
                }
            }
            int temp = nums[i];
            nums[i] = nums[max_index];
            nums[max_index] = temp;
            if (i== n-1) {
                result = nums[i];
                break;
            }
        }
        return result;
    }

    public static int findMin(int n, int[] nums){
        // write your code here
        int result = nums[0];
        for (int i = 0; i < nums.length; i++) {
            int min = nums[i];
            int min_index = i;
            for (int j = i; j < nums.length; j++) {
                if (min > nums[j]) {
                    min = nums[j];
                    min_index = j;
                }
            }
            int temp = nums[i];
            nums[i] = nums[min_index];
            nums[min_index] = temp;
            if (i== nums.length-n) {
                result = nums[i];
                break;
            }
        }
        return result;
    }

    public static int kthLargestElement(int n, int[] nums) {
        // write your code here
        int result = 0;
        if(n>nums.length/2){
            result = findMin(n,nums);
        }else{
            result = findMax(n,nums);
        }
        return result;
    }

    public static void main(String[] args) {
        int n = 105;
        //int nums[] = {1,3,4,2};
        int nums[] = {595240, 373125, 463748, 417209, 209393, 747977, 864346, 419023, 925673, 307640, 597868, 833339, 130763, 814627, 766415, 79576, 459038, 990103, 944521, 708820, 473246, 499960, 742286, 758503, 270229, 991199, 770718, 529265, 498975, 721068, 727348, 29619, 712557, 724373, 823743, 318203, 290432, 476213, 412181, 869308, 496482, 793858, 676162, 165869, 160511, 260864, 502521, 611678, 786798, 356560, 916620, 922168, 89350, 857183, 964051, 979979, 916565, 186532, 905289, 653307, 351329, 195491, 866281, 183964, 650765, 675046, 661642, 578936, 78684, 50105, 688326, 648786, 645823, 652329, 961553, 381367, 506439, 77735, 707959, 373271, 316194, 185079, 686945, 342608, 980794, 78777, 687520, 27772, 711098, 661265, 167824, 688245, 286419, 400823, 198119, 35400, 916784, 81169, 874377, 377128, 922531, 866135, 319912, 867697, 10904};
        //595240
        //10904
        System.out.println(kthLargestElement(n, nums));
    }
}