UVA 11134 fabled Rooks

Source: Internet
Author: User

Thinking about it:

The title is somewhat similar to the eight queens, but there is no limit in the direction of the diagonal, but a more restricted area. Because the problem of n max up to 5000, dare not rashly use backtracking. It can be learned that each rook in the title area is a rectangle, and each in the display, the x, Y axis is actually independent of each other, how to place the x-axis position does not affect the y-axis. So you can put the x-axis position, and then place the y-axis position, this way, the title looks like an interval-related greedy algorithm problem.

For x-axis interval, sort, rule: XR small row front, if XR same, then XL small row front. Select a small x whenever you choose the x position of an interval.

For the y-axis, this is the same way of handling.



2. Algorithmic Competition Introduction Classic (second edition)


At the beginning of the problem, the sorting ideas are wrong, the results are not found, until reference to other people's ideas (click here): if you press X as small as possible, sort must first by the XR small sort! Examples are:

The ranges of two zones A and B are [4,9] and [5,8] respectively. According to the collation, a should be ranked on the top of B:

(a) 4 5 6 7 8 9

(b) 5 6 7 8

If at this point 1-7 are already occupied by other vehicles, then a interval will be chosen to occupy 8. Interval B will return no solution. But actually a can account for 9, and B is 8.


/** * AC @ Sep 4th * Run time:0.009s */#include <bits/stdc++.h>using namespace std;struct Node {int XL, X    R, YL, yr; int x, Y, order;};/    /Globalconst int MAXN = + 50;int n;std::vector<node> v;bool read () {cin >> N;    if (N = = 0) {return false;    } v.clear ();    Node T;        for (int i = 0; i < N; ++i) {cin >> t.xl >> t.yl >> t.xr >> t.yr;        T.order = i;    V.push_back (t); } return true; BOOL Cmp_x (node &a, node &b) {return A.XR < B.XR | | (A.XR = = B.XR && A.XL < B.XL);} BOOL Cmp_x (node &a, node &b) {//return A.XL < B.XL | |  (A.XL = = B.xl && A.XR < B.XR);//}//This function was wrong used for sorting in this problem//CMP the R first, Then Lbool cmp_y (node &a, node &b) {return A.yr < B.yr | | (A.yr = = B.yr && a.yl < b.yl);} BOOL Cmp_order (node &a, node &b) {return a.order < B.order;} BOOL Is_possilE () {bool Vis[maxn] = {false};    Sort (V.begin (), V.end (), cmp_x);        for (int i = 0; i < N; ++i) {int L = V[I].XL, r = V[I].XR;        while (l <= R && Vis[l]) {++l;        } if (L > R) {return false;        } Vis[l] = true;    v[i].x = l;    } sort (V.begin (), V.end (), cmp_y);    Memset (Vis, false, sizeof (VIS));        for (int i = 0; i < N; ++i) {int L = v[i].yl, r = v[i].yr;        while (l <= R && Vis[l]) {++l;        } if (L > R) {return false;        } Vis[l] = true;    V[I].Y = l; } return true;    void output () {sort (V.begin (), V.end (), cmp_order); for (Std::vector<node>::iterator it = V.begin (); It! = V.end (); ++it) {cout << it->x << "" &    lt;< it->y << Endl;    }}void work () {if (is_possile () = = False) {cout << "impossible" << Endl;    } else {output (); }}int Main (int argc, char const *argv[]) {Ios::sync_with_stdio (false);    Cin.tie (0);    while (read ()) {work (); } return 0;}


UVA 11134 fabled Rooks

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: info-contact@alibabacloud.com and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.