UVA 1160 X-Plosives

并查集判断无向图是否有环

#include <stdio.h>
#include <string.h>
#include <set>
using namespace std;

const int max_n = 100005;
int merge_set[max_n];
set<int> visited;

void merge(int root_a, int root_b){
merge_set[root_a] = root_b;
}

int get_root(int child){
int cur_root, real_root;
int next_node;
cur_root = child;
while(1){
if(merge_set[cur_root] == cur_root)
break;
cur_root = merge_set[cur_root];
}
real_root = cur_root;
//compress the path
cur_root = child;
while(1){
if(cur_root == merge_set[cur_root])
break;
next_node = merge_set[cur_root];
merge_set[cur_root] = real_root;
cur_root = next_node;
}
return real_root;
}

int main(void){
int start, end;
int root_start, root_end;
int count;
int ret;

//freopen("input.dat", "r", stdin);

loop:
visited.clear();
count = 0;
while(scanf("%d", &start) != EOF){
if(start == -1){
printf("%d\n", count);
goto loop;
}
scanf("%d", &end);
if(visited.find(start) == visited.end()){
visited.insert(start);
merge_set[start] = start;
}
if(visited.find(end) == visited.end()){
visited.insert(end);
merge_set[end] = end;
}

root_start = get_root(start);
root_end = get_root(end);
if(root_start == root_end)
count++;
else
merge(root_start, root_end);
}
return 0;
}