POJ 2352 Stars 树状数组

原题链接

由于是求左下角的总数，且y输入从小到大，满足前缀和，故使用树状数组

#include <stdio.h>#include <string.h>#define lowbit(x) (x&(-x))const int maxn=15010,maxx=32010;int C[maxx],N,ans[maxn],x,y;///the level of starsint sum(int x){    int ans=0;    while(x>0){        ans+=C[x];        x-=lowbit(x);    }    return ans;}void add(int x){    while(x<=maxx){        C[x]++;        x+=lowbit(x);    }}int main(){    scanf("%d",&N);    memset(ans,0,sizeof(ans));    memset(C,0,sizeof(C));    for(int i=0;i<N;i++){        scanf("%d%d",&x,&y);        ans[sum(x+1)]++;///because x can equal 0, and array C need x>=1, so use x+1        add(x+1);    }    for(int i=0;i<N;i++)        printf("%d\n",ans[i]);    return 0;}