Blue Bridge Cup co-rooted plants disjoint-set

Successive questions papers together the roots of plants

Resource limitation
time limit: 2.0s memory limit: 256.0MB
problems described
　　w planet a plantation, is divided into small squares of m * n (m rows west direction, the north-south direction, n columns). Each frame house planted by co-rooted plants.
　　This plant has a feature that roots may extend along the north-south or east-west direction, with the plant to synthesize other lattice as a whole.

What if we told you there was a small grid between which the roots phenomenon, you can tell how much strain the roots of plants together in the park a total right?
Input format
　　number of rows of the first row, two integers m, n, separated by spaces, the grid represents the number of columns (1 <m, n <1000 ).
　　The next line, an integer k, k represents the following are data lines (0 <k <100000)
　　Next k rows, the first row two integers a, b, that number is a number of small lattice and small lattice b the root together.

Grid numbers line by line, from top to bottom, left to right number.
　　For example: 5 * 4 small lattice, ID:
　　. 1. 3 2 4
　　5. 6. 8. 7
　　. 9. 11 10 12 is
　　13 is 14 15 16
　　. 17. 19 18 is 20 is
sample input
5 4
16
2. 3
. 1 5
5. 9
4. 8
. 7. 8
. 9 10
10 . 11
. 11 12 is
10 14
12 is 16
14 18 is
. 17 18 is
15. 19
. 19 20 is
. 9 13 is
13 is. 17
sample output
5
Example Description
　　thereof with reference to the case of FIG engagement root

disjoint-set links Thought

#include<stdio.h>

int pre[1000*1000];
int count=0;

int find(int num){
	while(num!=pre[num]){
		num = pre[num];
	}
	return num;
}

void join(int num1,int num2){
	if(find(num2)!=find(num1))
		pre[find(num2)]=find(num1);
}

int main(){
	int m,n,k,num1,num2;
	scanf("%d %d",&m,&n);
	scanf("%d",&k);
	for(int i=1;i<=m*n;i++)
		pre[i]=i;
	for(int i=1;i<=k;i++){
		scanf("%d %d",&num1,&num2);
		join(num1,num2);
	}	
	for(int i=1;i<=m*n;i++)
		if(find(i)==i){
			count++;
		}
	printf("%d",count);
	return 0;
}