PAT(A) - 1118. Birds in Forest (25)
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Some scientists took pictures of thousands of birds in a forest. Assume that all the birds appear in the same picture belong to the same tree. You are supposed to help the scientists to count the maximum number of trees in the forest, and for any pair of birds, tell if they are on the same tree.
Input Specification:
Each input file contains one test case. For each case, the first line contains a positive number N (<= 104) which is the number of pictures. Then N lines follow, each describes a picture in the format:
K B1 B2 ... BK
where K is the number of birds in this picture, and Bi's are the indices of birds. It is guaranteed that the birds in all the pictures are numbered continuously from 1 to some number that is no more than 104.
After the pictures there is a positive number Q (<= 104) which is the number of queries. Then Q lines follow, each contains the indices of two birds.
Output Specification:
For each test case, first output in a line the maximum possible number of trees and the number of birds. Then for each query, print in a line "Yes" if the two birds belong to the same tree, or "No" if not.
Sample Input:43 10 1 22 3 44 1 5 7 83 9 6 4210 53 7Sample Output:
2 10YesNo
我刚开始想到的方法是散列,用两个数组进行存储,只拿了17分,后来想到并查集,AC了。看来甲级每次都会有并查集的题,这个我没怎么练过,多训练这方面吧!
#include <cstdio>#define MAX 10000int father[MAX];bool isRoot[MAX];int findFather( int x ) { int a = x; while( x != father[x] ) { x = father[x]; } while( a != father[a] ) { int z = a; a = father[a]; father[z] = x; } return x;}void Union( int a, int b ) { int faA = findFather( a ); int faB = findFather( b ); //printf( "%d %d\n", faA, faB ); if( faA != faB ) { father[faA] = faB; }}void init( int n ) { for( int i = 1; i <= n; i++ ) { father[i] = i; isRoot[i] = false; }}int main() { int n; scanf( "%d", &n ); init( MAX ); int max = -1; for( int i = 1; i <= n;i ++ ) { int m; scanf( "%d", &m ); for( int j = 1; j <= m; j++ ) { int index; int temp; scanf( "%d", &index ); if( j == 1 ) { temp = index; } if( max < index ) max = index; Union( temp, index ); } } for( int i = 1; i <= max; i++ ) { //printf( "根节点: %d\n", findFather( i ) ); isRoot[findFather( i )] = true; } int ans = 0; for( int i = 1; i <= max; i++ ) { if( isRoot[i] ) { ans++; } } printf( "%d %d\n", ans, max ); int q; scanf( "%d", &q ); for( int i = 0; i < q; i++ ) { int a, b; scanf( "%d%d", &a, &b ); int faA = findFather( a ); int faB = findFather( b ); if( faA == faB ) { printf( "Yes\n" ); } else { printf( "No\n" ); } } return 0;}
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