[POJ2352] Stars（树状数组）

传送门

先按照下标x排序，然后依次把y加入树状数组，边加入边统计即可。

注意下标re从零开始，需+1s

——代码

# include <iostream>
# include <cstdio>
# include <cstring>
# include <string>
# include <cmath>
# include <vector>
# include <map>
# include <queue>
# include <cstdlib>
# include <algorithm>
# define MAXN 32002
using namespace std;

inline int get_num() {
    int k = 0, f = 1;
    char c = getchar();
    for(; !isdigit(c); c = getchar()) if(c == '-') f = -1;
    for(; isdigit(c); c = getchar()) k = k * 10 + c - '0';
    return k * f;
}

int n;
int c[MAXN], ans[MAXN];
struct node
{
    int a, b;
}p[MAXN];

inline bool cmp(node x, node y)
{
    return x.a < y.a || (x.a == y.a && x.b < y.b);
}

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

inline int query(int x)
{
    int ans = 0;
    for(; x; x -= lowbit(x)) ans += c[x];
    return ans;
}

inline void add(int x)
{
    for(; x <= 32001; x += lowbit(x)) c[x] += 1;
}

int main()
{
    int i, t;
    n = get_num();
    for(i = 1; i <= n; i++)
    {
        p[i].a = get_num() + 1;
        p[i].b = get_num() + 1;
    }
    sort(p + 1, p + n + 1, cmp);
    for(i = 1; i <= n; i++)
    {
        t = query(p[i].b);
        add(p[i].b);
        ans[t]++;
    }
    for(i = 0; i < n; i++) printf("%d
", ans[i]);
    return 0;
}