【排序】

归并排序＜可求逆序对＞

 1 #include<iostream>
 2 #include<cstdio>
 3 using namespace std;
 4 long long n, a[1000100], c[1000100];
 5 long long ans=0;
 6 void merge(int l, int r)
 7 {
 8     if(l==r)    return ;
 9     int mid = (l + r) / 2;
10     merge(l,mid);
11     merge(mid+1,r);
12     int i = l, j = mid + 1, k = 1;
13     while (i <= mid && j <= r)
14     {
15         if (a[i] <= a[j])
16             c[k++] = a[i++];
17         else
18         {    c[k++] = a[j++];
19             ans+=mid-i+1;
20         }
21     }
22     while (i <= mid)    c[k++] = a[i++];
23     while (j <= r)    c[k++] = a[j++];    
24     for (i = l, k = 1; i <= r; i++)
25         a[i] = c[k++];
26     
27 }
28 int main()
29 {
30     cin >> n;
31     for (int i = 1; i <= n; i++)
32         cin >> a[i];
33     merge(1,n);
34     cout<<ans<<endl;
35     return 0;
36 }

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快速幂

 1 #include<iostream>
 2 using namespace std;
 3 //求b^P
 4 int b,p;
 5 void work()
 6 {
 7     long long ans=1;
 8     int t=p,s=b;
 9     while(t!=0)
10     {
11         if(t%2==1)  ans=ans*s;
12         t/=2;
13         s=s*s;
14     }
15 }
16 int main()
17 {
18     cin>>b>>p;
19     work();
20     cout<<ans<<endl;
21     return 0;
22 }

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二分

 1 #include<iostream>
 2 using namespace std;
 3 int a[10010],x;
 4 int find(int x)
 5 {
 6     int l=1,r=n;
 7     while(l+1<r)
 8     {
 9         int mid=(l+r)/2;
10         if(a[mid]==x)   return mid;
11         if(a[mid]>x)    r=mid;
12         if(a[mid]<x)    l=mid;
13     }
14     if(a[l]==x) return l;
15     if(a[r]==x) return r;
16     return -1;
17 }
18 int main()
19 {
20     cin>>x;
21     cout<<find(x)<<endl;
22     return 0;
23 }

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quicksort

 1 /*
 2 Language:c++;
 3 By Kaike;
 4 Date:2016.09.25;
 5 */
 6 #include<iostream>
 7 using namespace std;
 8 int n,a[10010];
 9 void quicksort(int l,int r)
10 {
11     if(l>r) return ;
12     int t=a[l];
13     int i=l,j=r;
14     while(i!=j)
15     {
16         while(a[j]>=temp && i<j)
17             j--;
18         while(a[i]<=temp && i<j)
19             i++;
20         if(i<j)
21             swap(a[i],a[j]);
22     }
23     a[l]=a[i];
24     a[i]=temp;
25     quicksort(l,i-1);
26     wuicksort(i+1,right);
27     return ;
28 }
29 int main()
30 {
31     cin>>n;
32     for(int i=1;i<=n;i++)
33         cin>>a[i];
34     quicksort(1,n);
35     for(int i=1;i<=n;i++)
36         cout<<a[i];
37     return 0;
38 }

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