[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\n", sum);    

    return 0;

}