11.2.2 example 11-2 UVA 1395 Slim Span (maximum-minimum as small as possible spanning tree)

Main topic:

Give you n points (n<=100), and then, let you find a spanning tree, making the maximum-minimum value of the Benquan as small as possible in the spanning tree.

Problem Solving Ideas:

Or according to the idea of the minimum spanning tree, start with all the edges according to the weight size, from small to large sort. Then, for an interval [l,r], each time we enumerate, if this [l,r] makes all n points connected, then the definition of their thinness is:

Maximum value-the minimum value. This slender degree must be <=cost[r]-cost[l]. So, we enumerate the L in order, each time we establish the minimum spanning tree with the edge of the [l,m] interval, if we can't satisfy the N-point Unicom, then return-1. Other times, it returns the value of Max-min, which instructs to find the smallest maximum-minimum value.

Code:

# include<cstdio># include<iostream># include<vector># include<algorithm>using namespace std    ; # define MAX 123# define INF 99999999int n,m;struct edge{int u,v,cost;    BOOL operator < (const Edge & A) const {return cost > a.cost; }};int f[max];vector<edge>edge;void Init () {for (int i = 0;i<= n;i++) f[i] = i;}    int getf (int x) {if (f[x]==x) return x;        else {int t = GETF (f[x]);        F[X] = t;    return f[x]; }}int Same (int x,int y) {return getf (x) ==getf (y);}    int Kruskal (int x) {init ();    int cnt = 0;    int _min = inf, _max =-1;        for (int i = X;i < m;i++) {Edge e = edge[i];        int u = edge[i].u;        int v = EDGE[I].V;        int UU = GETF (u);        int vv = GETF (v);            if (UU!=VV) {F[uu] = VV;            cnt++;            _min = min (_min,e.cost);        _max = max (_max,e.cost);      }} if (cnt==n-1)  return _max-_min; else return-1;}        int main (void) {while (scanf ("%d%d", &n,&m)!=eof) {if (n==0&&m==0) break;        Edge.clear ();            for (int i = 0;i < m;i++) {int a,b,c; scanf ("%d%d%d", &a,&b,&c);        Edge.push_back (Edge) {a,b,c});        } sort (Edge.begin (), Edge.end ());        int ans = inf;            for (int i = 0;i < m;i++) {int tmp = Kruskal (i);            if (tmp==-1) break;        ans = min (ans,tmp);        } if (Ans==inf) puts ("-1");    else printf ("%d\n", ans); } return 0;}

　　　　

11.2.2 example 11-2 UVA 1395 Slim Span (maximum-minimum as small as possible spanning tree)