AcWing 108. 奇数码问题

原题链接

考察：归并排序

n恒为奇数,所以左右上下移动不会改变逆序对的奇偶性.

 1 #include <iostream>
 2 #include <cstring>
 3 using namespace std;
 4 const int N = 250010;
 5 typedef long long LL;
 6 int n,a[N],b[N],tmp[N];
 7 void read(int c[])
 8 {
 9     for(int i=1,k =0;i<=n*n;i++)
10     {
11         int x;
12         scanf("%d",&x);
13         if(x) c[++k] = x;
14     }
15 }
16 LL merge(int l,int r,int a[])
17 {
18     if(l>=r) return 0;
19     int mid = l+r>>1;
20     LL ans = merge(l,mid,a);
21     ans+=merge(mid+1,r,a);
22     int i = l,j = mid+1,k= 0;
23     while(i<=mid&&j<=r)
24     {
25         if(a[i]<=a[j]) tmp[k++] = a[i++];
26         else tmp[k++] = a[j++],ans+=(long long)mid-i+1;
27     }
28     while(i<=mid) tmp[k++] = a[i++];
29     while(j<=r) tmp[k++] = a[j++];
30     for(int i=l;i<=r;i++) a[i] = tmp[i-l];
31     return ans;
32 }
33 int main()
34 {
35     while(scanf("%d",&n)!=EOF)
36     {
37         read(a);
38         read(b);
39         LL k = merge(1,n*n-1,a);
40         LL t = merge(1,n*n-1,b);
41         if(((k-t)%2)==0) puts("TAK");
42         else puts("NIE");
43     }
44     return 0;
45 }

 

 

2021.3.5 二刷WA了N次发现read函数里的c数组写成了a

         代码已经改成了二刷代码,这题的关键点在于左右不改变逆序对个数,上下移动逆序对偶数次变化.

posted @ 2021-01-06 09:38  acmloser  阅读(82)  评论(0)  编辑  收藏  举报