算法导论Java实现-插入排序

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package lhz.algorithm.chapter.two;

/**
 *  《插入排序 》，对少量元素进行排序的有效算法。
 *  《算法导论》原文摘要：
 * Insertion sort works the way many people sort a hand
 * of playing cards. We start with an empty left hand and the cards face down on
 * the table. We then remove one card at a time from the table and insert it
 * into the correct position in the left hand. To find the correct position for
 * a card, we compare it with each of the cards already in the hand, from right
 * to left, as illustrated in Figure 2.1. At all times, the cards held in the
 * left hand are sorted, and these cards were originally the top cards of the
 * pile on the table.
 * 伪代码如下：
 * for j<- 2 to length[A]
 *  do key <- A[j]
 *      >Insert A[j] into the sorted sequence A[1..j-1] （>符号代表后面的部分是注释）
 *      i <- j-1
 *      while i>0 and A[i]>key
 *          do A[i+1] <- A[i]
 *          i <- i-1
 *      A[i+1] <- key
 * 算法复杂度：n^2
 * @author lihzh(苦逼coder)
 * 本文地址：http://mushiqianmeng.blog.51cto.com/3970029/728821
 */
public class InsertionSort {

    private static int[] input = new int[] { 2, 1, 5, 4, 9, 8, 6, 7, 10, 3 };

    /**
     * @param args
     */
    public static void main(String[] args) {
        //从数组第二个元素开始排序，因为第一个元素本身肯定是已经排好序的
        for (int j = 1; j < input.length; j++) {// 复杂度 n
            int key = input[j];
            int i = j - 1;
            //依次跟之前的元素进行比较，如果发现比前面的原素小，则交换位置，最终完成排序。
            while (i >= 0 && input[i] > key) {//复杂度：1+2+...+(n-1)=Θ(n^2)
                input[i + 1] = input[i];
                input[i] = key;
                i--;
            }
        }
        /*
         * 所以最终复杂度为n*n=n^2。最优情况下（即都已经排列好的情况下），第二个n=1， 所以在最优情况下，复杂度为n。
         */
        // 打印数组
        printArray();
    }

    private static void printArray() {
        for (int i : input) {
            System.out.print(i + " ");
        }
    }
}

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