HDU-1301-Jungle Roads

描述

题解

代码

#include <iostream>
#include <cstring>

#define mem(a, b) memset(a, b, sizeof(a))

using namespace std;

/*
* Prim求MST
* 耗费矩阵cost[][]，初始化为INF，标号从0开始，0 ~ n－1
* 返回最小生成树的权值，返回-1表示原图不连通
*/

const int INF = 0x3f3f3f3f;
const int MAXN = 27;
bool vis[MAXN];
int lowc[MAXN];
int cost[MAXN][MAXN];

//  修正cost（添加边）
void updata(int x, int y, int v)
{
cost[x - 1][y - 1] = v;
cost[y - 1][x - 1] = v;
return ;
}

int Prim(int cost[][MAXN], int n)   //  0 ~ n - 1
{
int ans = 0;
memset(vis, false, sizeof(vis));
vis[0] = true;
for (int i = 1; i < n; i++)
{
lowc[i] = cost[0][i];
}
for (int i = 1; i < n; i++)
{
int minc = INF;
int p = -1;
for (int j = 0; j < n; j++)
{
if (!vis[j] && minc > lowc[j])
{
minc = lowc[j];
p = j;
}
}
if (minc == INF)
{
return -1;  //  原图不连通
}
ans += minc;
vis[p] = true;
for (int j = 0; j < n; j++)
{
if (!vis[j] && lowc[j] > cost[p][j])
{
lowc[j] = cost[p][j];
}
}
}
return ans;
}

int main(int argc, const char * argv[])
{
int N;
char village[2];    //  字符串读入防止缓冲区出问题
int num;
int len;

while (cin >> N && N != 0)
{
mem(cost, 0x3f);
mem(vis, 0);

for (int i = 1; i < N; i++)
{
scanf("%s%d", village, &num);
int temp = village[0] - 'A' + 1;
//            cout << temp << '\n';
for (int j = 0; j < num; j++)
{
scanf("%s%d", village, &len);
updata(temp, village[0] - 'A' + 1, len);
}
}

int ans = Prim(cost, N);

cout << ans << '\n';
}

return 0;
}

参考