【树状数组】POJ 2352 Stars

/**
 *  @author           johnsondu
 *  @time             2015-8-22
 *  @type             Binary Index Tree
 *                      ignore the coordinate of y and 
 *                      process as 1D conditions.
 *  @url              http://poj.org/problem?id=2352
 */

#include <iostream>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <cstring>
#include <string>
#include <stack>
#include <queue>
#include <map>
#include <vector>

using namespace std;

const int N = 15005;
const int M = 32010;
int level[N], c[M];

int lowbit(int x) {
    return (x & (-x)) ;
}

// 向上更新
void update(int x, int v) {
    while(x < M) {
        c[x] += v;
        x += lowbit(x);
    }
}

// 获取当前节点及以下的值的个数
int getSum(int x) {
    int sum = 0;
    while(x > 0) {
        sum += c[x];
        x -= lowbit(x);
    }
    return sum;
}

int main()
{
    int n, x, y;
    scanf ("%d", &n);
    memset(level, 0, sizeof(level));
    memset(c, 0, sizeof(c));
    for(int i = 1; i <= n; i ++) {
        scanf("%d%d", &x, &y);
        ++ level[getSum(x + 1)];
        update(x+1, 1);
    }

    for(int i = 0; i < n; i ++) {
        cout << level[i] << endl;
    }

    return 0;
}

附一篇经典翻译，学习 树状数组  http://www.hawstein.com/posts/binary-indexed-trees.html