667 Beautiful Arrangement II

667. Beautiful Arrangement II​
1. Question
Given two integersnandk, you need to construct a list which containsndifferent positive integers ranging from1tonand 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 exactlykdistinct integers.
If there are multiple answers, print any of them.
Example 1:
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Input: n = 3, k = 1
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Output: [1, 2, 3]
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Explanation:
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The [1, 2, 3] has three different positive integers ranging from 1 to 3, and the [1, 1] has exactly 1 distinct integer: 1.
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Example 2:
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Input: n = 3, k = 2
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Output: [1, 3, 2]
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Explanation:
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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.
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Note:
1.Thenandkare in the range 1 <= k < n <= 10^4.
2. Implementation
思路:
(1) 当K等于1时，显然直接将1-n升序放在数组即可
(2) 当K大于1时，我们可以发现K最大的可能值是n - 1，比如当n = 5时，数组为
1， 2， 3， 4，5
得到最多4个差值得数组为
1， 5， 2， 4，3
差: 4, 3, 2, 1
我们发现规律是，将1 - n的数交错放在数组里，比如先放1，再放n, 然后放2，之后放n - 1，以此类推
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class Solution {
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    public int[] constructArray(int n, int k) {
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        if (n == 0 || k <= 0 || k >= n) {
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            return new int[0];
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        }
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​
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        int[] res = new int[n];
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        int start = 1, end = n;
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​
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        for (int i = 0; start <= end; i++) {
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            // 当 K 等于 1时，将1-n的数字直接升序放在数组即可
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            if (k== 1) {
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                res[i] = start;
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                ++start;
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            }
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            // 否则将start和end交错放在数组里
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            else {
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                if (k % 2 != 0) {
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                    res[i] = start;
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                    ++start;
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                }
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                else {
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                    res[i] = end;
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                    --end;
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                }
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                --k;
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            }
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        }
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        return res;
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    }
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}
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3. Time & Space Complexity
时间复杂度O(n), 空间复杂度O(n)

789 Escape The Ghosts

359 Logger Rate Limiter

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Contents

667. Beautiful Arrangement II

1. Question

2. Implementation

3. Time & Space Complexity

667. Beautiful Arrangement II​

1. Question

2. Implementation

3. Time & Space Complexity

667. Beautiful Arrangement II