"Convex Shell" "Hnoi 2008" "Bzoj 1007" Horizontal Visible Line

1007: [HNOI2008] Horizontal visible Line

Time Limit: 1 Sec  Memory Limit: 162 MBSubmit: 4567  Solved: 1686

Description

There are n linear l1,l2 on the Xoy Cartesian plane,... Ln, if the Y value is positive infinity down, you can see a sub-segment of Li, it is said that Li is visible, otherwise li is covered.
For example, for a line:
L1:y=x; L2:y=-x; L3:y=0
Then L1 and L2 are visible, and L3 are covered.
gives a line of N, expressed as a form of y=ax+b (| a|,| b|<=500000), and the N line 22 does not coincide. Find all the visible lines.

Input

The first behavior n (0 < n < 50000), the next n-line input Ai,bi

Output

From small to large output visible line number, 22 is separated by a space, the last number must also have a space behind

Sample Input

3-1 01 00 0

Sample Output

1 2

Exercises

At first glance, I think this is a half-plane, but after careful examination of the problem found that it is not so complicated, just to maintain a lower convex shell is good.

Code:

#include <iostream>#include <cstdio>#include <cstdlib>#include <cmath>#include <cstring>#include <algorithm>using namespace STD;#define N 50100structe{intXu,a,b;} E[n],ee[n];intn,top=0, num=0, Z[n];intIn () {intx=0;CharCh=getchar ();BOOLf=true; while(ch<' 0 '|| Ch>' 9 '){if(ch=='-') f=false;    Ch=getchar (); } while(ch>=' 0 '&& ch<=' 9 ') x=x*Ten+ch-' 0 ', Ch=getchar ();if(!f) X=-x;returnx;}BOOLCMP1 (E x,e y) {returnX.A&GT;Y.A;}BOOLCMP2 (intXintY) {returnEe[x].xu<ee[y].xu;}DoubleJiao (E x,e y) {return(Double)((Double) (Y.B-X.B)/(Double) (X.A-Y.A));}intMain () {n=in (); z[++top]=1; for(intI=1; i<=n;    i++) E[i].xu=i,e[i].a=in (), E[i].b=in (); Sort (e+1, e+n+1, CMP1); for(intI=1; i<=n; i++) {if(e[i].a!=ee[i-1].A) Ee[++num]=e[i];Else if(e[i].b>ee[num].b) ee[num]=e[i]; } for(intI=2; i<=num; i++) { while(top>=2){DoubleX1=jiao (ee[z[top-1]],ee[i]);DoubleX2=jiao (Ee[z[top]],ee[i]);if(x1<=x2+1e-6) top--;Else  Break;    } z[++top]=i; } sort (z+1, z+top+1, CMP2); for(intI=1; i<=top; i++)printf("%d", Ee[z[i]].xu);return 0;}

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"Convex Shell" "Hnoi 2008" "Bzoj 1007" Horizontal Visible Line