Prim 算法:
// Prim算法:
#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
const int N = 510;
int n, m, INF = 0x3f3f3f3f;
int g[N][N];
int dist[N];
bool st[N];
int prim()
{
memset(dist, 0x3f, sizeof dist);
int res = 0;
for(int i = 0; i < n; i ++ )
{
int t = -1;
for(int j = 1; j <= n; j ++ )
if(!st[j] && (t == -1 || dist[t] > dist[j]))
t = j;
if(i && dist[t] == INF) return INF;
if(i) res += dist[t];
for(int j = 1; j <= n; j ++ ) dist[j] = min(dist[j], g[t][j]);
st[t] = true;
}
return res;
}
int main()
{
scanf("%d%d", &n, &m);
memset(g, 0x3f, sizeof g);
while(m -- )
{
int a, b, c;
scanf("%d%d%d", &a, &b, &c);
g[a][b] = g[b][a] = min(g[a][b], c);
}
int t = prim();
if(t == INF) puts("impossible");
else printf("%d\n", t);
return 0;
}
Kruskal 算法:
// Kruskal算法:
#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
const int N = 200010;
int n, m, INF = 0x3f3f3f3f;
int p[N];
struct Edge{
int a, b, w;
bool operator< (const Edge &W) const
{
return w < W.w;
}
}edges[N];
int find(int x)
{
if(p[x] != x) p[x] = find(p[x]);
return p[x];
}
int main()
{
scanf("%d%d", &n, &m);
for(int i = 0; i < m; i ++ )
{
int a, b, w;
scanf("%d%d%d", &a, &b, &w);
edges[i] = {a, b, w};
}
sort(edges, edges + m);
for(int i = 1; i <= n; i ++ ) p[i] = i;
int res = 0, cnt = 0;
for(int i = 0; i < m; i ++ )
{
int a = edges[i].a, b = edges[i].b, w = edges[i].w;
a = find(a), b = find(b);
if(a != b)
{
p[a] = b;
res += w;
cnt ++ ;
}
}
if(cnt < n - 1) puts("impossible");
else printf("%d\n", res);
return 0;
}
染色法 :
// 染色法:
#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
const int N = 100010, M = 200010;
int n, m;
int h[N], e[M], ne[M], idx;
int color[N];
void add(int a, int b)
{
e[idx] = b; ne[idx] = h[a], h[a] = idx ++ ;
}
bool dfs(int u, int c)
{
color[u] = c;
for(int i = h[u]; i != -1; i = ne[i])
{
int j = e[i];
if(!color[j])
{
if(!dfs(j, 3 - c)) return false; // 2表示黑色
}
else if(color[j] == c) return false;
}
return true;
}
int main()
{
scanf("%d%d", &n, &m);
memset(h, -1, sizeof h);
while(m -- )
{
int a, b;
scanf("%d%d", &a, &b);
add(a, b), add(b, a);
}
bool flag = true;
for(int i = 1; i <= n; i ++ )
{
if(!color[i])
{
if(!dfs(i, 1)) // 1表示白色
{
flag = false;
break;
}
}
}
if(flag) puts("Yes");
else puts("No");
return 0;
}
匈牙利算法 :
// 匈牙利算法:
#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
const int N = 510, M = 100010;
int n1, n2, m;
int h[N], e[M], ne[M], idx;
int match[N];
bool st[N];
void add(int a, int b)
{
e[idx] = b, ne[idx] = h[a], h[a] = idx ++ ;
}
bool find(int x)
{
for(int i = h[x]; i != -1; i = ne[i])
{
int j = e[i];
if(!st[j])
{
st[j] = true;
if(match[j] == 0 || find(match[j]))
// 当这个女的没有男的匹配、或者女的匹配的那个男的可以找其他女的
{
match[j] = x;
return true;
}
}
}
return false;
}
int main()
{
scanf("%d%d%d", &n1, &n2, &m);
memset(h, -1, sizeof h);
while(m -- )
{
int a, b;
scanf("%d%d", &a, &b);
add(a, b);
}
int res = 0;
for(int i = 1; i <= n1; i ++ )
{
memset(st, false, sizeof st);
if(find(i)) res ++ ;
}
printf("%d\n", res);
return 0;
}
那……最短路呢?
最短路的写了没有保存起来,今天学了这个加上上次有保存的那些就随便发了一下
O