【Codeforces 404C】Restore Graph

每个节点的度数不超过k
让你重构一个图
使得这个图满足从某个点开始到其他点的最短路满足输入的要求

【题解】

把点按照dep的值分类
显然只能由dep到dep+1连边
设cnt[dep]表示到起点的距离为dep的点的集合
如果cnt[dep].size>cnt[dep+1].size
那么只要把dep层的前cnt[dep+1].size个点和dep+1层的点连就好了
否则
只能让dep层的点每个多连几个dep+1层的点了

【代码】

import java.io.*;

import java.util.*;

public class Main {

    static InputReader in;

    static PrintWriter out;

    public static void main(String[] args) throws IOException{

        //InputStream ins = new FileInputStream("E:\\rush.txt");

        InputStream ins = System.in;

        in = new InputReader(ins);

        out = new PrintWriter(System.out);

        //code start from here

        new Task().solve(in, out);

        out.close();

    }

    static int N = (int)1e5;

    static class Task{

    	class Pair{

    		int x,y;

    		public Pair(int x,int y) {

    			this.x = x;

    			this.y = y;

    		}

    	}

        int n,k;

        ArrayList<Integer> g[] = new ArrayList[N+10];

        ArrayList<Pair> ans = new ArrayList<>();

        public void solve(InputReader in,PrintWriter out) {

        	for (int i = 0;i <= N;i++) g[i]=new ArrayList<Integer>();

        	n = in.nextInt();k = in.nextInt();

        	for (int i = 1;i <= n;i++) {

        		int d;

        		d = in.nextInt();

        		g[d].add(i);

        	}

        	if ((int)g[0].size()>1) {

        		out.println(-1);

        	}else {

        		for (int i = 1;i <= n;i++)

        			if ((int)g[i].size()>0 && g[i-1].isEmpty()) {

        				out.println(-1);

        				return;

        			}

        		for (int i = 1;i <= n;i++) {

        			if (g[i].isEmpty()) break;

        			int x = g[i].size();

        			int y = g[i-1].size();

        			//out.println(x+" "+y);

        			if (y>=x) {

        				for (int j = 0;j < x;j++) {

        					ans.add(new Pair(g[i-1].get(j),g[i].get(j)));

        				}

        				int ma = 1;

        				if (i-1>=1) {

        					ma = 2;

        				}

        				if (ma>k) {

        					out.println(-1);

        					return;

        				}

        			}else {

        				//y<x

        				int need = x/y;

        				if (x%y!=0) need++;

        				int ma = need;

        				//out.println(ma);

        				if (i-1>=1) ma++;

        				if (ma>k) {

        					out.println(-1);

        					return;

        				}

        				for (int j = 0;j < x;j++) {

        					int now = j;

        					now = now % y;

        					ans.add(new Pair(g[i-1].get(now),g[i].get(j)));

        				}

        			}

        		}

        		out.println((int)ans.size());

        		for (int i = 0;i < ans.size();i++) {

        			out.println(ans.get(i).x+" "+ans.get(i).y);

        		}

        	}

        }

    }

    static class InputReader{

        public BufferedReader br;

        public StringTokenizer tokenizer;

        public InputReader(InputStream ins) {

            br = new BufferedReader(new InputStreamReader(ins));

            tokenizer = null;

        }

        public String next(){

            while (tokenizer==null || !tokenizer.hasMoreTokens()) {

                try {

                tokenizer = new StringTokenizer(br.readLine());

                }catch(IOException e) {

                    throw new RuntimeException(e);

                }

            }

            return tokenizer.nextToken();

        }

        public int nextInt() {

            return Integer.parseInt(next());

        }

    }

}

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【Codeforces 404C】Restore Graph

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