这次没看答案，把去年的代码重新推翻再写了下，确实感觉到很多可以优化的地方，然后这个算法没我想象中的那么难，网络流24题可以安排上了，两个版本
版本1：这个版本是用邻接矩阵，但是后来发现完全可以用前向星
#include <bits/stdc++.h> using namespace std; #define limit (1000 + 5)//防止溢出 #define INF 0x3f3f3f3f #define inf 0x3f3f3f3f3f #define lowbit(i) i&(-i)//一步两步 #define EPS 1e-6 #define FASTIO ios::sync_with_stdio(false);cin.tie(0); #define ff(a) printf("%d\n",a ); #define pi(a,b) pair<a,b> #define rep(i, a, b) for(ll i = a; i <= b ; ++i) #define per(i, a, b) for(ll i = b ; i >= a ; --i) #define MOD 988244353 #define FOPEN freopen("C:\\Users\\tiany\\CLionProjects\\acm_01\\data.txt", "rt", stdin) #define FOUT freopen("C:\\Users\\tiany\\CLionProjects\\acm_01\\dabiao.txt", "wt", stdout) typedef long long ll; typedef unsigned long long ull; ll read(){ ll sign = 1, x = 0;char s = getchar(); while(s > '9' || s < '0' ){if(s == '-')sign = -1;s = getchar();} while(s >= '0' && s <= '9'){x = (x << 3) + (x << 1) + s - '0';s = getchar();} return x * sign; }//快读 void write(ll x){ if(x < 0) putchar('-'),x = -x; if(x / 10) write(x / 10); putchar(x % 10 + '0'); } int n,m; int g[limit][limit]; int dist[limit],vis[limit]; int fa[limit]; void init(){ memset(dist, INF, sizeof(dist)); memset(vis, 0 , sizeof(vis)); } int spfa(){ queue<int>q; init(); vis[1] = 1; dist[1] = 0; q.push(1); fa[n] = -1; while (q.size()){ int u = q.front(); q.pop(); vis[u] = 0; rep(v ,1,n){ if(dist[u] + 1 < dist[v] && g[u][v] > 0){ dist[v] = dist[u] + 1; fa[v] = u; if(!vis[v]){ vis[v] = 1; q.push(v); } } } } return ~fa[n]; } int max_flow; void dinic(){ while (spfa()){ int min_flow = INF; for(int u = n ; u - 1 ; u = fa[u]){ min_flow = min(min_flow, g[fa[u]][u]); } max_flow += min_flow; for(int u = n ; u - 1 ; u = fa[u]){ g[fa[u]][u] -= min_flow; g[u][fa[u]] += min_flow; } } } int main() { #ifdef LOCAL FOPEN; #endif while (cin>>m>>n) { m = read(), n = read(); memset(g, 0 , sizeof(g)); rep(i, 1, m) { int x = read(), y = read(), flow = read(); g[x][y] += flow; } dinic(); write(max_flow),putchar('\n'); } return 0; }前向星版本：
#include <bits/stdc++.h> using namespace std; #define limit (1000000 + 5)//防止溢出 #define INF 0x3f3f3f3f #define inf 0x3f3f3f3f3f #define lowbit(i) i&(-i)//一步两步 #define EPS 1e-6 #define FASTIO ios::sync_with_stdio(false);cin.tie(0); #define ff(a) printf("%d\n",a ); #define pi(a,b) pair<a,b> #define rep(i, a, b) for(ll i = a; i <= b ; ++i) #define per(i, a, b) for(ll i = b ; i >= a ; --i) #define MOD 988244353 #define FOPEN freopen("C:\\Users\\tiany\\CLionProjects\\acm_01\\data.txt", "rt", stdin) #define FOUT freopen("C:\\Users\\tiany\\CLionProjects\\acm_01\\dabiao.txt", "wt", stdout) typedef long long ll; typedef unsigned long long ull; ll read(){ ll sign = 1, x = 0;char s = getchar(); while(s > '9' || s < '0' ){if(s == '-')sign = -1;s = getchar();} while(s >= '0' && s <= '9'){x = (x << 3) + (x << 1) + s - '0';s = getchar();} return x * sign; }//快读 void write(ll x){ if(x < 0) putchar('-'),x = -x; if(x / 10) write(x / 10); putchar(x % 10 + '0'); } int n,m,vs,ve; int head[limit],cnt; int dist[limit],fa[limit],vis[limit],pre[limit]; struct node{ int to, next, flow, w; }edge[limit<<1]; void add(int u, int v, int flow, int w = 1){ edge[cnt].to = v; edge[cnt].flow = flow; edge[cnt].w = w; edge[cnt].next = head[u]; head[u] = cnt++; } void init(int flag = 0){ if(flag){ memset(dist, INF, sizeof(dist)); memset(vis, 0 , sizeof(vis)); }else{ memset(head, -1, sizeof(head)); cnt = 0; } } int spfa(){ queue<int>q; init(1); dist[vs] = 0; vis[vs] = 1; q.push(vs); pre[ve] = -1; while (q.size()){ int u = q.front(); q.pop(); vis[u] = 0; for(int i = head[u]; ~i; i = edge[i].next){ int v = edge[i].to, w = edge[i].w; int stream = edge[i].flow; if(dist[u] + w < dist[v] && stream > 0){ dist[v] = dist[u] + w; pre[v] = i; fa[v] = u; if(!vis[v]){ vis[v] = 1; q.push(v); } } } } return ~pre[ve]; } int max_flow,min_cost; void dinic(){ while (spfa()){ int min_flow = INF; for(int i = ve; i != vs; i = fa[i]){ min_flow = min(min_flow, edge[pre[i]].flow); } max_flow += min_flow; min_cost += dist[ve] * min_flow; for(int i = ve; i != vs; i = fa[i]){ edge[pre[i]].flow -= min_flow; edge[pre[i] ^ 1].flow += min_flow; } } } int main() { #ifdef LOCAL FOPEN; #endif while(cin>>n>>m){ vs= 1, ve =m; init(); rep(i, 1, n){ int x= read(),y = read(), floww = read(); if(~head[x] || edge[head[x]].flow == 0) { add(x, y, floww); add(y, x, 0); }else{ edge[head[x]].flow += floww; } } max_flow = 0; dinic(); printf("%d\n", max_flow); } return 0; }