poj2352——Stars

题意：给你一些按y轴优先排列的坐标点，求这个点的左下方的数有多少个。输出的时候，再转换下即可。

思路：因为的按y轴优先排序的，所以用线段树解决，每次查询(0,x)之间的数，即为这个坐标的左下方的数。并将(x,y)插入线段树。

#include<iostream> #include<cstdio> #include<cstring> using namespace std; struct node { int left,right,step; }tree[97000]; int level[15008]; int n; int find(int index,int left,int right) { if(left<=tree[index].left&&tree[index].right <=right) return tree[index].step ; int mid =(tree[index].left +tree[index].right )>>1; if(mid>=right) return find(index*2,left,right); else if(left>mid) return find(index*2+1,left,right); else { int m=find(index*2,left,right); int n=find(index*2+1,left,right); return m+n; } } void add(int index,int left,int right) { tree[index].step ++; if(tree[index].left ==tree[index].right ) return ; int mid=(tree[index].left +tree[index].right )>>1; if(mid>=right) add(index*2,left,right); else add(index*2+1,left,right); } void create(int index,int left,int right) { tree[index].left =left; tree[index].right =right; tree[index].step =0; if(left==right) return ; int mid=(left+right)>>1; create(index*2,left,mid); create(index*2+1,mid+1,right); } int main() { int i,x,y,sum; memset(level,0,sizeof(level)); create(1,0,32000); scanf("%d",&n); for(i=0;i<n;i++) { scanf("%d%d",&x,&y); sum=0; sum+=find(1,0,x); level[sum]++; add(1,0,x); } for(i=0;i<n;i++) printf("%d\n",level[i]); return 0; }