poj2352 Stars

求每个星星坐下方的星星个数,题目已经按y的左边递增的顺序排好

简单的区间统计, 一定要注意 i可以为0的情况的存在!!

(树状数组)

#include <stdio.h>
#include <string.h>
#define N 15000 + 10
int c[32000+10];
int n, Max;

inline int lowbit(int x) {return (x&-x);}
void modify(int i,int d) {for(; i<=Max+1; i+=lowbit(i)) c[i]+=d;}
int sum(int i) {int ret = 0; for(; i>0; i-=lowbit(i)) ret+=c[i]; return ret;}

int main()
{
    int i, y;
    int x[N], ans[N];
    while(scanf("%d",&n)!=EOF) {
        Max = 0;
        for(i=0; i<n; ++i) {
            scanf("%d%d",&x[i],&y);
            if(Max < x[i]) Max = x[i];
        }
        memset(c, 0, sizeof c );
        memset(ans, 0, sizeof ans );
        for(i=0; i<n; ++i) {
            ans[sum(x[i]+1)]++;
            modify(x[i]+1, 1);
        }
        for(i=0; i<n; ++i) {
            printf("%d\n",ans[i]);
        }
    }
    return 0;
}


你可能感兴趣的:(poj2352 Stars)