http://acm.hdu.edu.cn/showproblem.php?pid=2689

C++版本一

線段樹

/* *@Author: STZG *@Language: C++ */ //#include <bits/stdc++.h> #include<iostream> #include<algorithm> #include<cstdlib> #include<cstring> #include<cstdio> #include<string> #include<vector> #include<bitset> #include<queue> #include<deque> #include<stack> #include<cmath> #include<list> #include<map> #include<set> //#define DEBUG #define RI register int using namespace std; typedef long long ll; //typedef __int128 lll; const int N=100000+10; const int MOD=1e9+7; const double PI = acos(-1.0); const double EXP = 1E-8; const int INF = 0x3f3f3f3f; int t,n,m,k,q; int ans,cnt,flag,temp; ll tree[N<<2]; void pushup(int rt){tree[rt]=tree[rt<<1]+tree[rt<<1|1]; } void updata(int l,int r,int rt,int L,int C){if(l==r){tree[rt]+=C;return;}int mid=(l+r)>>1;if(L<=mid)updata(l,mid,rt<<1,L,C);else updata(mid+1,r,rt<<1|1,L,C);pushup(rt); } ll query(int l,int r,int rt,int L,int R){if(l>=L&&r<=R){return tree[rt];}int mid=(l+r)>>1;ll res=0;if(L<=mid)res+=query(l,mid,rt<<1,L,R);if(R>mid)res+=query(mid+1,r,rt<<1|1,L,R);return res; } int main() { #ifdef DEBUGfreopen("input.in", "r", stdin);//freopen("output.out", "w", stdout); #endifwhile(~scanf("%d",&n)){memset(tree,0,sizeof(tree));ans=0;for(int i=1;i<=n;i++){scanf("%d",&t);ans+=query(1,n,1,t+1,n);updata(1,n,1,t,1);}cout << ans << endl;}//cout << "Hello world!" << endl;return 0; }

C++版本二

樹狀數組

#include <bits/stdc++.h> using namespace std; typedef long long ll; inline int read() {int x=0,f=1;char ch=getchar();while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();}return x*f; } inline void write(int x) {if(x<0){putchar('-');x=-x;}if(x>9){write(x/10);}putchar(x%10+'0'); } const int N=1001; int n; int num[N]; int c[N]; struct node {int x;int id; }q[N] ; bool cmp(node a,node b) {return a.x<b.x; } int lowbit(int x) {return x&(-x); } int getsum(int x) {int s=0;while(x>0){s+=c[x];x-=lowbit(x);}return s; } void add(int x,int y) {while(x<=n){c[x]+=y;x+=lowbit(x);} } int main() {while(scanf("%d",&n)!=EOF){memset(c,0,sizeof(c));memset(num,0,sizeof(num));for(int i=1;i<=n;i++){scanf("%d",&q[i].x);q[i].id=i;}sort(q+1,q+1+n,cmp);for(int i=1;i<=n;i++){num[q[i].id]=i;}int sum = 0;for(int i=1;i<=n;i++){add(num[i],1);sum+=getsum(n)-getsum(num[i]);}printf("%d\n",sum);}return 0; }

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