Review the tree-like array

It's a pretty interesting question:

Http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=501&page=show_ problem&problem=4174

Learn a few things:

1. Construction of tree-like array c[i], a c[i]=s[i]-s[i-lowbit (i)]; This is a practice that has been used. Now learn a new, direct add (I,a[i]), and (S[i] for a[1] to A[i)

2, prefixes and ideas, the sum of the tree array itself is based on the idea of prefix and. The number of numbers smaller than a certain number, by opening a large number of space + suffix array, efficient statistics out of a number of small number

3, in fact, I think through this question. The ability to make an O (nlogn) sorting algorithm. Of course, the place that is not good is only can be whole number, but should be able to solve with vector+map?

Stick to your own code first. , because the code behind the LRJ Daniel is too concise ...

#include <iostream> #include <cstdio> #include <cstring> #include <algorithm> #include < Queue> #include <functional>using namespace std; #define MAXN 20010#define SIZE 100015int a[maxn],sma[size],c[ Size],s[size],e[size],tot[size];int n,mmax;int lowbit (int i) {return I & (-i);} int sum (int i) {int ans=0; for (; I>0;i-=lowbit (i)) ans+=c[i]; return ans;} void Add (int x, int d) {while (x <= SIZE) {c[x] + = D; x + = Lowbit (x); }}void Init () {memset (c,0,sizeof (c)); memset (A,0,sizeof (a)); memset (sma,0,sizeof (SMA)); Memset (s,0,sizeof (s)); memset (E,0,sizeof (e)); memset (tot,0,sizeof (TOT));} int main () {//freopen ("La4329.txt", "R", stdin); int t; Long long ans; scanf ("%d", &t); while (t--) {mmax=0; ans=0; Init (); scanf ("%d", &n); for (int i=1;i<=n;i++) {scanf ("%d", &a[i]); Mmax=max (Mmax,a[i]); Add (a[i],1); C[i]=sum (a[i]-1); E[a[i]]=1; Sma[a[i]]=sum (a[i]-1); } memset (C,0,sizeof (c)); for (int i=1;i<=mmax;i++) {s[i] =s[i-1]+e[i]; C[i]=s[i]-s[i-lowbit (i)]; Tot[i]=sum (i-1); }/////////////////////////for (int i=1;i<=n;i++)//{//printf ("sma[a[%d]" =%d tot (%d ) =%d\n ", I,sma[a[i]],a[i],tot[a[i]]); }///////////////////////for (int i=1;i<=n;i++) {int tmp = Tot[a[i]]-sma[a[i]];/*a[i ] The number of smaller than a[i] */ans+= (Long Long) tmp* (I-1-sma[a[i]) + (Long Long) sma[a[i]]* (n-i-tmp); } printf ("%lld\n", ans); } return 0;}

Standard process

LA4329 Ping pong//Rujia liu#include<cstdio> #include <vector>using namespace std;//inline int lowbit (int x {return x& (x^ (x-1));} inline int lowbit (int x) {return x&-x;} struct Fenwicktree {int n; Vector<int> C; void Resize (int n) {this->n = n; C.resize (n); } void Clear () {Fill (C.begin (), C.end (), 0);} // ???? A[1]+a[2]+...+a[x] (x<=n) int sum (int x) {int ret = 0; while (x > 0) {ret + = c[x]; x-= Lowbit (x); } return ret; }//a[x] + = d (1<=x<=n) void Add (int x, int d) {while (x <= N) {c[x] + = D; x + = Lowbit (x); }}};const int maxn = 20000 + 5;int N, A[maxn], C[MAXN], D[MAXN]; Fenwicktree F;int Main () {freopen ("La4329.txt", "R", stdin); int T; scanf ("%d", &t); while (t--) {scanf ("%d", &n); int Maxa = 0; for (int i = 1; I <= n; i++) {scanf ("%d", &a[i]), Maxa = Max (Maxa, A[i]);} F.resize (MAXA); F.clear (); for (int i = 1; I <= n; i++) {F.add (a[i], 1); C[i] = f.sum (a[i]-1); } f.clear (); for (int i = n; I >= 1; i--) {F.add (a[i], 1); D[i] = f.sum (a[i]-1); } long long ans = 0; for (int i = 1; I <= n; i++) ans + = (long Long) c[i]* (N-i-d[i]) + (Long Long) (i-c[i]-1) *d[i]; printf ("%lld\n", ans); } return 0;}

Tree-like array LA 4329 Asian Games Beijing Division