leetcode-667-Beautiful-Arrangement-II

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描述

Given two integers n and k, you need to construct a list which contains n different positive integers ranging from 1 to n and obeys the following requirement:
Suppose this list is [a1, a2, a3, … , an], then the list [|a1 - a2|, |a2 - a3|, |a3 - a4|, … , |an-1 - an|] has exactly k distinct integers.

If there are multiple answers, print any of them.

Example 1:

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Input: n = 3, k = 1
Output: [1, 2, 3]
Explanation: The [1, 2, 3] has three different positive integers ranging from 1 to 3, and the [1, 1] has exactly 1 distinct integer: 1.

Example 2:

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Input: n = 3, k = 2
Output: [1, 3, 2]
Explanation: The [1, 3, 2] has three different positive integers ranging from 1 to 3, and the [2, 1] has exactly 2 distinct integers: 1 and 2.

Note:

  1. The n and k are in the range $1 <= k < n <= 10^4$.

分析

1…n 这样的序列，能组成的最大的差值为 n-1, n-2, … 1, 0, 因为 $1 <= k < n <= 10^4$，所以结果肯定是存在的，只是我们需要构造一个这样的序列。根据 k 的值依次写入最大，最小值，每次写入后 k 自减1，当 k 等于1时，按照升序取剩余的数即可。

n = 3, k = 2

3, 1, 2

n = 3, k = 1
1, 2, 3

解决方案1(Java)

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class Solution {
    public int[] constructArray(int n, int k) {
        int[] result = new int[n];
        int count = 0;
        int left = 1, right = n;
        while (left <= right) {
            if (k > 1) {
                result[count++] = k-- % 2 == 1? left++ : right--;
            } else {
                result[count++] = left++;
            }
        }
        return result;
    }
}

相关问题

(M) Beautiful Arrangement

题目来源