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  • LC 667. Beautiful Arrangement II

    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 kdistinct integers.

    If there are multiple answers, print any of them.

    Example 1:

    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:

    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 <= 104.

    Runtime: 28 ms, faster than 39.80% of C++ online submissions for Beautiful Arrangement II.

    构造题

    最小,k=1是顺序或者倒序的排列。

    最大,k=n-1是依此从两头挑数的排列。

    根据k来判断要排多少个头尾数。

    #include <vector>
    #include <iostream>
    using namespace std;
    class Solution {
    public:
      vector<int> constructArray(int n, int k) {
        int tmp = k/2;
        vector<int> ret;
        int idx = 1;
        while(tmp){
          ret.push_back(idx);
          ret.push_back(n+1 - idx);
          idx++;
          tmp--;
        }
        if(k % 2 == 1){
          for(int i = idx; i<= n+1-idx; i++) ret.push_back(i);
        }else for(int i=n+1-idx; i>=idx; i--) ret.push_back(i);
        return ret;
      }
    };
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  • 原文地址:https://www.cnblogs.com/ethanhong/p/10190519.html
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