解题思路

• 满足的序列即为环
• 若图上有环，则代价为0
• 若无环，则在图上已有的边在添加一条回边可形成环
• 对所有的点由小到大排序
• 由于环的大小可以为2
• 初值设为，先不管最小点之间是否有边，反正不会更劣
• 通过拓扑排序找环，在找环的过程中，看能否添一条边，代价更小
• 若拓扑不能访问到所有的点则有环
• 添边，则按照拓扑顺序，维护每个点能被访问的点中，值最小的与其连边形成环，判断代价

 

import java.io.*;
import java.math.BigInteger;
import java.util.Arrays;
import java.util.BitSet;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.PriorityQueue;
import java.util.Queue;
import java.util.Random;
import java.util.Stack;
import java.util.StringTokenizer;
import java.util.Vector;public class Main{static long md=(long)998244353;static long Linf=Long.MAX_VALUE/2;static int inf=Integer.MAX_VALUE/2;staticclass Edge{int fr,to,nxt;public Edge(int u,int v) {fr=u;to=v;}}static Edge[] e;static int[] head;static int cnt=0;static void addEdge(int fr,int to) {cnt++;e[cnt]=new Edge(fr, to);e[cnt].nxt=head[fr];head[fr]=cnt;}static class Node{int x;long y;public Node(int X,long Y) {x=X;y=Y;}}public static void main(String[] args) throws IOException{AReader input=new AReader();PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));int n=input.nextInt();int m=input.nextInt();e=new Edge[m+1];head=new int[n+1];cnt=0;long[] a=new long[n+1];long[] b=new long[n+1];for(int i=1;i<=n;++i) {long y=input.nextLong();a[i]=y;b[i]=y;}Arrays.sort(a,1,n+1);//拓扑排序int[] in=new int[n+1];for(int i=1;i<=m;++i) {int u=input.nextInt();int v=input.nextInt();addEdge(u, v);in[v]++;}Queue<Integer> q=new LinkedList<Integer>();int tot=0;long[] c=new long[n+1];Arrays.fill(c, Linf);for(int i=1;i<=n;++i) {if(in[i]==0) {q.add(i);}}while(!q.isEmpty()) {int x=q.peek();q.poll();tot++;for(int i=head[x];i>0;i=e[i].nxt) {int v=e[i].to;c[v]=Math.min(Math.min(c[x], b[x]), c[v]);//维护每个点能被访问点中最小的值、//c[x]不包含自己，在更新其连边时要加上in[v]--;if(in[v]==0) {q.add(v);}}}if(tot<n) {//判环out.println(0);}else {//无环long ans=(a[1]+a[2])*2;for(int i=1;i<=n;++i) {long res=b[i]+c[i];ans=Math.min(ans, res);}out.print(ans);}out.flush();out.close();}//System.out.println();//out.println();staticclass AReader{BufferedReader bf;StringTokenizer st;BufferedWriter bw;public AReader(){bf=new BufferedReader(new InputStreamReader(System.in));st=new StringTokenizer("");bw=new BufferedWriter(new OutputStreamWriter(System.out));}public String nextLine() throws IOException{return bf.readLine();}public String next() throws IOException{while(!st.hasMoreTokens()){st=new StringTokenizer(bf.readLine());}return st.nextToken();}public char nextChar() throws IOException{//确定下一个token只有一个字符的时候再用return next().charAt(0);}public int nextInt() throws IOException{return Integer.parseInt(next());}public long nextLong() throws IOException{return Long.parseLong(next());}public double nextDouble() throws IOException{return Double.parseDouble(next());}public float nextFloat() throws IOException{return Float.parseFloat(next());}public byte nextByte() throws IOException{return Byte.parseByte(next());}public short nextShort() throws IOException{return Short.parseShort(next());}public BigInteger nextBigInteger() throws IOException{return new BigInteger(next());}public void println() throws IOException {bw.newLine();}public void println(int[] arr) throws IOException{for (int value : arr) {bw.write(value + " ");}println();}public void println(int l, int r, int[] arr) throws IOException{for (int i = l; i <= r; i ++) {bw.write(arr[i] + " ");}println();}public void println(int a) throws IOException{bw.write(String.valueOf(a));bw.newLine();}public void print(int a) throws IOException{bw.write(String.valueOf(a));}public void println(String a) throws IOException{bw.write(a);bw.newLine();}public void print(String a) throws IOException{bw.write(a);}public void println(long a) throws IOException{bw.write(String.valueOf(a));bw.newLine();}public void print(long a) throws IOException{bw.write(String.valueOf(a));}public void println(double a) throws IOException{bw.write(String.valueOf(a));bw.newLine();}public void print(double a) throws IOException{bw.write(String.valueOf(a));}public void print(char a) throws IOException{bw.write(String.valueOf(a));}public void println(char a) throws IOException{bw.write(String.valueOf(a));bw.newLine();}}
}