给出每条边的下界 求最小流
板题
提供两个板子代码 虽然这个题 第一个比较快
但在loj上https://loj.ac/problem/117
的板题 第一个1700+ms
第二个才600+ms 用输入挂后400+ms
#include <iostream> #include <cstdio> #include <sstream> #include <cstring> #include <map> #include <cctype> #include <set> #include <vector> #include <stack> #include <queue> #include <algorithm> #include <cmath> #include <bitset> #define rap(i, a, n) for(int i=a; i<=n; i++) #define rep(i, a, n) for(int i=a; i<n; i++) #define lap(i, a, n) for(int i=n; i>=a; i--) #define lep(i, a, n) for(int i=n; i>a; i--) #define rd(a) scanf("%d", &a) #define rlld(a) scanf("%lld", &a) #define rc(a) scanf("%c", &a) #define rs(a) scanf("%s", a) #define rb(a) scanf("%lf", &a) #define rf(a) scanf("%f", &a) #define pd(a) printf("%d ", a) #define plld(a) printf("%lld ", a) #define pc(a) printf("%c ", a) #define ps(a) printf("%s ", a) #define MOD 2018 #define LL long long #define ULL unsigned long long #define Pair pair<int, int> #define mem(a, b) memset(a, b, sizeof(a)) #define _ ios_base::sync_with_stdio(0),cin.tie(0) //freopen("1.txt", "r", stdin); using namespace std; const int maxn = 1e5 + 10, INF = 0x7fffffff; int n, m, s, t; int head[maxn], cur[maxn], vis[maxn], nex[maxn << 1], in[maxn]; int d[maxn]; int cnt; struct node { int u, v; int c; }Node[maxn << 1]; void add_(int u, int v, int c) { Node[cnt].u = u; Node[cnt].v = v; Node[cnt].c = c; nex[cnt] = head[u]; head[u] = cnt++; } void add(int u, int v, int c) { add_(u, v, c); add_(v, u, 0); } bool bfs() { queue<int> Q; mem(d, 0); Q.push(s); d[s] = 1; while(!Q.empty()) { int u = Q.front(); Q.pop(); for(int i = head[u]; i != -1; i = nex[i]) { int v = Node[i].v; if(!d[v] && Node[i].c > 0) { d[v] = d[u] + 1; Q.push(v); if(v == t) return 1; } } } return d[t] != 0; } int dfs(int u, int cap) { int ret = 0; if(u == t || cap == 0) return cap; for(int &i = cur[u]; i != -1; i = nex[i]) { int v = Node[i].v; if(d[v] == d[u] + 1 && Node[i].c > 0) { int V = dfs(v, min(cap, Node[i].c)); Node[i].c -= V; Node[i ^ 1].c += V; ret += V; cap -= V; if(cap == 0) break; } } if(cap > 0) d[u] = -1; return ret; } int Dinic() { int ans = 0; while(bfs()) { memcpy(cur, head, sizeof head); ans += dfs(s, INF); } return ans; } int tranf(string x) { if(x == "+") return 1; if(x == "-") return n + 2; int ans = 0, len = x.size(); for(int i = 0; i < len; i++) { ans += (x[i] - '0') * pow(10, len - i - 1); } return ans + 1; } int main() { int w; string u, v; int u_, v_; while(~scanf("%d%d", &n, &m)) { if(n == 0 && m == 0) break; mem(head, -1); cnt = 0; mem(in, 0); int sum = 0; s = 0, t = n + 3; rap(i, 1, m) { // scanf(" %c %c %d", &u, &v, &w); cin >> u >> v >> w; u_ = tranf(u); v_ = tranf(v); add(u_, v_, INF - w); in[v_] += w; in[u_] -= w; } for(int i = 1; i <= n + 2; i++) { if(in[i] > 0) { sum += in[i]; add(s, i, in[i]); } else add(i, t, -in[i]); } int ans = Dinic(); add(n + 2, 1, INF); ans += Dinic(); if(sum == ans) cout << Node[head[(n + 2)] ^ 1].c << endl; else cout << "impossible" << endl; } return 0; }
#include <iostream> #include <cstdio> #include <sstream> #include <cstring> #include <map> #include <cctype> #include <set> #include <vector> #include <stack> #include <queue> #include <algorithm> #include <cmath> #include <bitset> #define rap(i, a, n) for(int i=a; i<=n; i++) #define rep(i, a, n) for(int i=a; i<n; i++) #define lap(i, a, n) for(int i=n; i>=a; i--) #define lep(i, a, n) for(int i=n; i>a; i--) #define rd(a) scanf("%d", &a) #define rlld(a) scanf("%lld", &a) #define rc(a) scanf("%c", &a) #define rs(a) scanf("%s", a) #define rb(a) scanf("%lf", &a) #define rf(a) scanf("%f", &a) #define pd(a) printf("%d ", a) #define plld(a) printf("%lld ", a) #define pc(a) printf("%c ", a) #define ps(a) printf("%s ", a) #define MOD 2018 #define LL long long #define ULL unsigned long long #define Pair pair<int, int> #define mem(a, b) memset(a, b, sizeof(a)) #define _ ios_base::sync_with_stdio(0),cin.tie(0) //freopen("1.txt", "r", stdin); using namespace std; const int maxn = 1e5 + 10, INF = 0x7fffffff; int n, m, s, t; int head[maxn], cur[maxn], vis[maxn], nex[maxn << 1], in[maxn]; int d[maxn]; int cnt; struct node { int u, v, bz; int c; }Node[maxn << 1]; void add_(int u, int v, int c, int bz) { Node[cnt].u = u; Node[cnt].v = v; Node[cnt].c = c; Node[cnt].bz = bz; nex[cnt] = head[u]; head[u] = cnt++; } void add(int u, int v, int c, int bz) { add_(u, v, c, bz); add_(v, u, 0, bz); } bool bfs() { queue<int> Q; mem(d, 0); Q.push(s); d[s] = 1; while(!Q.empty()) { int u = Q.front(); Q.pop(); for(int i = head[u]; i != -1; i = nex[i]) { int v = Node[i].v; if(!d[v] && Node[i].c > 0) { d[v] = d[u] + 1; Q.push(v); if(v == t) return 1; } } } return d[t] != 0; } int dfs(int u, int cap) { int ret = 0; if(u == t || cap == 0) return cap; for(int &i = cur[u]; i != -1; i = nex[i]) { int v = Node[i].v; if(d[v] == d[u] + 1 && Node[i].c > 0) { int V = dfs(v, min(cap, Node[i].c)); Node[i].c -= V; Node[i ^ 1].c += V; ret += V; cap -= V; if(cap == 0) break; } } if(cap > 0) d[u] = -1; return ret; } int Dinic() { int ans = 0; while(bfs()) { memcpy(cur, head, sizeof head); ans += dfs(s, INF); } return ans; } int tranf(string x) { if(x == "+") return 1; if(x == "-") return n + 2; int ans = 0, len = x.size(); for(int i = 0; i < len; i++) { ans += (x[i] - '0') * pow(10, len - i - 1); } return ans + 1; } int main() { int w; string u, v; int u_, v_; while(~scanf("%d%d", &n, &m)) { if(n == 0 && m == 0) break; mem(head, -1); cnt = 0; mem(in, 0); int sum = 0; s = 0, t = n + 3; rap(i, 1, m) { // scanf(" %c %c %d", &u, &v, &w); cin >> u >> v >> w; u_ = tranf(u); v_ = tranf(v); add(u_, v_, INF - w, 1); in[v_] += w; in[u_] -= w; } for(int i = 1; i <= n + 2; i++) { if(in[i] > 0) { sum += in[i]; add(s, i, in[i], 0); } else add(i, t, -in[i], 0); } add(n + 2, 1, INF, 0); if(sum != Dinic()) ps("impossible"); else { sum = Node[head[n + 2] ^ 1].c; for(int i = 0; i < cnt; i++) { if(!Node[i].bz) Node[i].v = 0; } head[s] = head[t] = -1; s = n + 2; t = 1; cout << sum - Dinic() << endl; } } return 0; }