• Minimum Sum of Array(map迭代器)


    You are given an array a consisting of n integers a1, ..., an. In one operation, you can choose 2 elements ai and aj in which ai is divisible by aj and transform ai to aj.

    A number x is said to be divisible by a number y if x can be divided by y and the result is an exact whole number. For example, 15 is divisible by 3, because 15÷ 3 = 5 exactly, but 9 is not divisible by 2 because 9÷ 2 is 4 with 1 left over.

    Your task is to find the minimum sum of the array a that can be obtained by making as many transform operations as you want. Can you?

    Input

    The first line contains an integer T (1 ≤ T ≤ 100) specifying the number of test cases.

    The first line of each test case contains an integer n (1 ≤ n ≤ 105), in which n is the size of array a. Then a line follows containing n integers a1, ..., an (1 ≤ ai ≤ 106), giving array a.

    The sum of n overall test cases does not exceed 3 × 106.

    Output

    For each test case, print a single line containing the minimum sum of the array a that can be obtained after making as many transform operations as you want.

    Example
    Input
    1
    5
    2 2 3 6 6
    Output
    11




    题目意思:有一个长度为n的数组,对于数组中的两个元素x,y如果满足y%x==0,则可以将y转换成x,求经过多次变换后数组的前n项和最小是多少。
    由于数据量较大我们选择了map这一容器来去重。对容器中的每一个元素遍历,开始我的打算是将每一个元素的因子都拆分,再按照从小到大的顺序来一一枚举因子(因为如果容器中有元素等于交小的因子
    替换后得到的答案就是最小的),可惜超时了,于是寻求另一种方法来解决。我同学给我提供了一个新的思路,我们在求某一个数的因子的时候,为了优化算法,降低时间复杂度,会采用一种方法,比如求
    12的因子的时候,我们从1到12逐个遍历,知道2是12的因子,那么也能得到12/2=6也是12的因子;知道了3是12的因子,那么也同时得到了4也是12的因子。这里也是一样的,我们也是先依次去从小的因子
    出发,找小的因子的过程中也找到了其对应的比其大的因子。如果小因子不存在,再看看对应的较大的那个因子是否存在,存在的话就保存下来。之后也是这样增大因子,重复这个过程,要是存在对应的交大的因子就更新保存的结果,这些较小的因子都找过了依旧不满足条件,那么就找那个保存的那个较大的因子。
    还需要注意的是mp.erase(),当在迭代器中调用这个函数的话,需要先返回上一个迭代器,不然指针会变为一个野指针(可参考链表理解)。
     1 #include<cstdio>
     2 #include<cstring>
     3 #include<algorithm>
     4 #include<map>
     5 #define LL long long int
     6 using namespace std;
     7 int main()
     8 {
     9     int t,flag,flag1;
    10     LL i,j,a,n,k;
    11     LL ans,x;
    12     map<LL,LL>mp;
    13     map<LL,LL>::iterator it;
    14     scanf("%d",&t);
    15     while(t--)
    16     {
    17         mp.clear();
    18         scanf("%lld",&n);
    19         for(i=0;i<n;i++)
    20         {
    21             scanf("%lld",&a);
    22             mp[a]++;
    23         }
    24         flag=0;
    25         ans=0;
    26         for(it=mp.begin();it!=mp.end();it++)
    27         {
    28             k=it->first;
    29             if(k==1)///出现1
    30             {
    31                 flag=1;
    32                 break;
    33             }
    34             flag1=0;
    35             x=0;
    36             for(i=2;i*i<=k;i++)
    37             {
    38                 if(k%i==0)
    39                 {
    40                     if(mp.count(i))
    41                     {
    42                         mp[i]+=mp[k];
    43                         it--;
    44                         mp.erase(k);
    45                         flag1=1;
    46                         break;
    47                     }
    48                     else if(mp.count(k/i))
    49                     {
    50                         x=k/i;
    51                     }
    52                 }
    53             }
    54             if(!flag1)
    55             {
    56                 if(x)
    57                 {
    58                     mp[x]+=mp[k];
    59                     it--;
    60                     mp.erase(k);
    61                 }
    62             }
    63         }
    64         if(flag)
    65         {
    66             printf("%lld
    ",n);
    67         }
    68         else
    69         {
    70             for(it=mp.begin();it!=mp.end();it++)
    71             {
    72                 ans+=it->second*it->first;
    73             }
    74             printf("%lld
    ",ans);
    75         }
    76     }
    77     return 0;
    78 }
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  • 原文地址:https://www.cnblogs.com/wkfvawl/p/9387634.html
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