[wikioi]最优布线问题

http://wikioi.com/problem/1231/

Kruskal+并查集。comp函数里面如果用const引用的话，可以减少copy。并查集find的时候是递归找父亲的根。无他。

#include <cstdio>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <memory.h>
#define MAX(a, b) a>b?a:b
#define LEN 100005
using namespace std;

struct Edge {
    int a;
    int b;
    int val;
};

int n, m;
Edge edges[LEN];
int father[LEN];

int find(int x) {
    if (father[x] != x)
        father[x] = find(father[x]);
    return father[x];
}

void merge(int x, int y) {
    father[find(x)] = find(y);
}

void init() {
    memset(father, 0, sizeof(father));
    memset(edges, 0, sizeof(edges));
    scanf("%d%d", &n, &m);
    for (int i = 0; i < m; i++) {
        scanf("%d%d%d", &edges[i].a, &edges[i].b, &edges[i].val);
    }
    for (int i = 1; i <= n; i++) {
        father[i] = i;
    }
}

bool comp(const Edge &a, const Edge &b) {
    return a.val < b.val;
}
 
int main()
{
    init();
    sort(edges, edges+m, comp);
    long long sum = 0;
    for (int i = 0; i < m; i++) {
        int x = edges[i].a;
        int y = edges[i].b;
        if (find(x) != find(y)) {
            sum += edges[i].val;
            merge(x, y);
        }
    }
    printf("%lld
", sum);    
    return 0;
}