POJ 2352 树状数组(Binary Indexed Tree)

题意：每个点的的左下角的点的个数为当前点的层次，打印出处于每个层次的点的个数
思路：
    每输入一个点累加当前点左边的点的个数，记录层次。(log(x))并更新x座标下的点的个数(log(N));

#include <iostream> #include <cstdio> #include <cstring> using namespace std; const int MAXN=32016; int CurrentNum[MAXN+10]; int c[MAXN+10];//树状数组 int level[MAXN+10]; void insert(int x) { while(x<=MAXN) { c[x]++; x+=x&(x^(x-1)); } } int sum(int x) { int ans=0; while(x>0) { ans+=c[x]; x-=x&(x^(x-1)); } return ans; } int main() { int n; int x,y; int i; while(scanf("%d",&n)!=EOF) { memset(c,0,sizeof(c)); memset(level,0,sizeof(level)); for(i=0;i<n;i++) { scanf("%d %d",&x,&y); x++; y++; level[sum(x)]++;//累加当前层的个数 insert(x);//更新 } for(i=0;i<n;i++) { printf("%d/n",level[i]); } } return 0; }

附录：　
    题意：
Stars
Time Limit: 1000MS        Memory Limit: 65536K
Total Submissions: 16639        Accepted: 7209

Description
Astronomers often examine star maps where stars are represented by points on a plane and each star has Cartesian coordinates. Let the level of a star be an amount of the stars that are not higher and not to the right of the given star. Astronomers want to know the distribution of the levels of the stars.

For example, look at the map shown on the figure above. Level of the star number 5 is equal to 3 (it's formed by three stars with a numbers 1, 2 and 4). And the levels of the stars numbered by 2 and 4 are 1. At this map there are only one star of the level 0, two stars of the level 1, one star of the level 2, and one star of the level 3.

You are to write a program that will count the amounts of the stars of each level on a given map.

Input
The first line of the input file contains a number of stars N (1<=N<=15000). The following N lines describe coordinates of stars (two integers X and Y per line separated by a space, 0<=X,Y<=32000). There can be only one star at one point of the plane. Stars are listed in ascending order of Y coordinate. Stars with equal Y coordinates are listed in ascending order of X coordinate.

Output
The output should contain N lines, one number per line. The first line contains amount of stars of the level 0, the second does amount of stars of the level 1 and so on, the last line contains amount of stars of the level N-1.

Sample Input

5
1 1
5 1
7 1
3 3
5 5

Sample Output

1
2
1
1
0