【代碼超詳解】POJ 1789 Truck History（Kruskal 算法）

一、題目描述

二、算法分析說明與代碼編寫指導

三、AC 代碼

#include<cstdio>
#include<algorithm>
#pragma warning(disable:4996)
using namespace std;
template<size_t n> class union_find {
private:
	unsigned root[n]; int rank[n];
public:
	union_find<n>() { init(); }
	union_find<n>(const bool& WannaInit) { if (WannaInit == true)init(); }
	void init() {
		fill(rank, rank + n, 1); for (unsigned i = 0; i < n; ++i)root[i] = i;
	}
	void init(const size_t& _n) {
		fill(rank, rank + _n, 1); for (unsigned i = 0; i < _n; ++i)root[i] = i;
	}
	unsigned find_root(const unsigned& v) {
		unsigned r = v, t = v, u;
		if (t == root[v])return v;
		while (r != root[r]) { r = root[r]; }
		while (t != r) { u = root[t]; root[t] = r; t = u; }
		return r;
	}
	void path_compress() const { for (unsigned i = 0; i < n; ++i)find_root(i); }
	void merge(unsigned u, unsigned v) {
		unsigned fu = find_root(u), fv = find_root(v); int d = rank[fu] - rank[fv];
		if (d < 0) { swap(fu, fv); swap(u, v); }
		else if (d == 0)++rank[fu];
		root[fv] = fu;
	}
	void merge_no_path_compression(const unsigned& u, const unsigned& v) {
		root[v] = u; if (rank[u] == rank[v])++rank[u];
	}
	void merge_directly(const unsigned& u, const unsigned& v) { root[v] = u; }
	unsigned _rank(const unsigned& v) const { return rank[find_root(v)]; }
	size_t size() const { return n; }
};
const unsigned nmax = 4000;
struct edge { unsigned u, v, w; };
inline bool cmp(const edge& e, const edge& f) { return e.w < f.w; }
unsigned N, n, q; union_find<nmax> u(false); edge e[nmax * (nmax - 1) / 2], * E; char s[nmax][8];
inline unsigned dist(const char* const s, const char* const t) {
	const char* u = s + 8; unsigned r = 0;
	for (const char* i = s, *j = t; i != u; ++i, ++j) { if (*i != *j)++r; }
	return r;
}
int main() {
	for (;;) {
		scanf("%u", &n); if (n == 0)return 0;
		u.init(n); E = e; q = 0; N = 0; getchar();
		for (unsigned i = 0; i < n; ++i) {
			gets_s(s[i]);
			for (unsigned j = 0; j < i; ++j) { E->u = i; E->v = j; E->w = dist(s[i], s[j]); ++E; }
		}
		sort(e, E, cmp); --n; E = e;
		for (; N < n; ++E) {
			if (u.find_root(E->u) != u.find_root(E->v)) { u.merge(E->u, E->v); ++N; q += E->w; }
		}
		printf("The highest possible quality is 1/%u.\n", q);
	}
}