poj1328 Radar Installation Range greedy

Main topic:

Select as few points as possible on the X axis as the center of the circle with a radius of D. So that these circles can cover all the points.

Ideas:

Convert each point to the x-axis. That is, the range of positions that can cover the center of the point [A, b]. Then follow each point corresponding to a from small to large sort. The 1th requires special treatment, and we assign a value of r=b0. That is to make the center of the first circle the horizontal axis as large as possible. Then traverse the remaining points. For the I point, if the AI of the point is greater than r, you need to add a circle with the center of BI; Otherwise, update R to the value of R and bi small.

Code:

1#include <iostream>2#include <cstdio>3#include <cstring>4#include <cmath>5#include <algorithm>6 using namespacestd;7 8 Const intN =1010;9 structnodeTen { One     Doublex, y; A     Doubleb; - }p[n]; - BOOLCMP (node n1,node n2) the { -     returnn1.a<n2.a; - } - intMain () + { -     //freopen ("Test.txt", "R", stdin); +     intN,d,ca=1; A      while(SCANF ("%d%d", &n,&d)!=eof&&N) at     { -         inti; -         BOOLflag=0; -          for(i=0; i<n;i++) -         { -scanf"%LF%LF",&p[i].x,&p[i].y); in             if(p[i].y>d) flag=1; -         } toprintf"Case %d:", ca++); +         if(flag) printf ("-1\n"); -         Else the         { *              for(i=0; i<n;i++) $             {Panax Notoginseng                 Doublex=p[i].x,y=p[i].y; -P[I].A=-SQRT (d*d-y*y) +x; theP[I].B=SQRT (d*d-y*y) +x; +             } ASort (p,p+n,cmp); the             Doubler=p[0].b; +             intans=1; -              for(i=1; i<n;i++) $             { $                 if(p[i].a>R) { -R=p[i].b; -ans++; the                 } -                 if(P[i].b<r) r=p[i].b;Wuyi             } theprintf"%d\n", ans); -         } Wu     } -     return 0; About}

View Code

poj1328 Radar Installation Range greedy