Codevs 1222 Letter and envelope problem (the perfect match of the binary chart)

1222 Letter and Envelope questions

Title Description Description

Mr. John wrote n letters in the evening , and wrote n envelopes accordingly to install the letter, ready to send it. But the next day John 's son, John Small, took all the n letters out of the envelope. Unfortunately, Small John was unable to properly put the letter back into the envelope.

The n letters supplied by small John are numbered 1,2, ...,N,and n envelopes are numbered 1,2, ..., n. Suppose small John can provide a set of information: The letter I is definitely not in the envelope J . Please program help small John to correctly load the letter back into the envelope as much as possible.

Enter a description Input Description

The first line of the n file is an integer n(n≤). Letters and envelopes are numbered 1,2, ...,n.

n each row in the next row has 2 of the number i and J, indicating that the letter I letter is definitely not in the first J envelope. The last line of the file is 2 0, which indicates the end.

Output description Output Description

Each line in the output file has 2 numbers I and J, indicating that the letter I is bound to be in the J Envelope. Please press the letter number I from small to large sequential output. If you are unsure of any correspondence to properly load the envelope, the output is "none".

Sample input Sample Input

3

1 2

1 3

2 1

0 0

Sample output Sample Output

1 1

Ideas

The perfect Match of the binary graph.

First match to see if there is a perfect match, none is none. If there is an enumeration that deletes an edge in a perfect match, the edge is output if the point does not match after the edge is deleted, if none is none.

1#include <cstdio>2#include <cstring>3#include <queue>4#include <vector>5 #definefor (A,B,C) for (int a= (b);a< (c); a++)6 using namespacestd;7 8 Const intMAXN = -+Ten;9 Ten BOOLT[MAXN]; One intLKX[MAXN],LKY[MAXN]; A //Lkx represents the Y-node that matches the X-node lky represents the X-node that matches the Y-node . - intn,m; - intA[MAXN][MAXN]; the  - BOOLMatchintu) { -      for(intv=1; v<=n;v++) -         if(! A[U][V] &&!T[v]) { +t[v]=1; -             if(!lky[v] | |match (Lky[v])) { +Lky[v]=u, lkx[u]=v; A                 return true; at             } -         } -     return false; - } -  - intMain () { inscanf"%d",&n); -     intu,v; to      while(SCANF ("%d%d", &u,&v) = =2&& (u&&v)) +a[u][v]=1; -     intans=0; the      for(intI=1; i<=n;i++) { *memset (T,0,sizeof(T)); $         if(Match (i)) ans++;Panax Notoginseng     } -     if(ans!=n) printf ("none\n"); the     Else { +         BOOLflag=0; A          for(intI=1; i<=n;i++) { the             intv=Lkx[i]; +a[i][v]=1;  -lkx[i]=0, lky[v]=0; $memset (T,0,sizeof(T)); $             if(!match (i)) { -printf"%d%d\n", i,v); -Lkx[i]=v,lky[v]=i; flag=1;//Recovery the             } -a[i][v]=0;//RecoveryWuyi         } the         if(!flag) puts ("none\n"); -     } Wu     return 0; -}

Codevs 1222 Letter and envelope problem (the perfect match of the binary chart)