POJ 2391 -- Ombrophobic Bovines

#include<cstdio>
#include<cstring>
#include<queue>
#include<iostream>
#include<vector>
#define Min(a,b) ((a)<(b)?(a):(b))
#define Max(a,b) ((a)>(b)?(a):(b))
#define INF 0x3f3f3f3f
#define IN64 0x3f3f3f3f3f3f3f3fll
using namespace std;
const int N=410, M=82800;
int n, m, s, t, top;
int head
, gap
, cur
, dis
, vis
, pre
, num1[210], num2[210];
long long line[210][210];

struct Edge{
int to, next, flow;
Edge(int _to = 0, int _next = 0, int _flow = 0):to(_to), next(_next), flow(_flow){}
}edge[M];

void Floyd(){
for(int k = 1; k <= n; ++k){
for(int i = 1; i <= n; ++i){
for(int j = 1; j <= n; ++j)
line[i][j] = Min(line[i][j], line[i][k] + line[k][j]);
}
}
}
void Addedge(int from, int to, int flow){
edge[top] = Edge(to, head[from], flow);
head[from] = top++;
edge[top] = Edge(from, head[to], 0);
head[to] = top++;
}

void Bfs(){
queue<int> q;
memset(gap, 0, sizeof(gap));
memset(dis, -1, sizeof(dis));
gap[0] = 1; dis[t] = 0; q.push(t);
while(!q.empty()){
int u = q.front(); q.pop();
for(int i = head[u]; i+1; i = edge[i].next){
if(dis[edge[i].to] == -1){
dis[edge[i].to] = dis[u] + 1;
gap[dis[edge[i].to]] ++;
q.push(edge[i].to);
}
}
}
}

int Sap(){
Bfs();
memset(pre, -1, sizeof(pre));
for(int i = s; i <= t; ++i) cur[i] = head[i];
int u = s, cur_flow, max_flow = 0, neck, tmp;
while(dis[s] <= t){
if(u == t){
cur_flow = INF;
for(int i = s; i != t; i = edge[cur[i]].to){
if(cur_flow > edge[cur[i]].flow){
cur_flow = edge[cur[i]].flow;
neck = i;
}
}
for(int i = s; i != t; i = edge[cur[i]].to){
tmp = cur[i];
edge[tmp].flow -= cur_flow;
edge[tmp^1].flow += cur_flow;
}
max_flow += cur_flow;
u = neck;
}
int i;
for(i = cur[u]; i + 1; i = edge[i].next){
if(edge[i].flow && dis[u] == dis[edge[i].to] + 1) break;
}
if(i != -1){
cur[u] = i;
pre[edge[i].to] = u;
u = edge[i].to;
}else{
if(--gap[dis[u]] == 0) break;
cur[u] = head[u];
int mindis = t;
for(i = head[u]; i + 1; i = edge[i].next)
if(edge[i].flow && mindis > dis[edge[i].to]) mindis = dis[edge[i].to];
dis[u] = mindis + 1;
gap[dis[u]] ++;
if(u != s) u = pre[u];
}
}
return max_flow;
}

int main(){
while(~scanf("%d%d", &n, &m)){
for(int i = 1; i <= n; ++i){
for(int j = 1; j <= n; ++j) line[i][j] = IN64;
line[i][i] = 0;
}
s = 0, t = n * 2 + 1;
int u, v, val, cnt = 0;
long long sum = 0;
for(int i = 1; i <= n; ++i) scanf("%d%d", &num1[i], &num2[i]), cnt += num1[i];
for(int i = 1; i <= m; ++i){
scanf("%d%d%d", &u, &v, &val);
if(line[u][v] > val) line[u][v] = line[v][u] = val;
}
Floyd();
for(int i = 1; i <= n; ++i)
for(int j = 1; j <= n; ++j){
if(i != j && line[i][j] != IN64) sum = Max(sum, line[i][j]);
}
long long low = 0, high = sum, mid, ans = -1;
while(low <= high){
mid = (low + high) / 2;
memset(head, -1, sizeof(head));
top = 0;
for(int i = 1; i <= n; ++i){
Addedge(s, i, num1[i]);
Addedge(i+n, t, num2[i]);
for(int j = 1; j <= n; ++j){
if(line[i][j] <= mid) Addedge(i, j+n, INF);
}
}
int res = Sap();
if(res == cnt) ans = mid, high = mid - 1;
else low = mid + 1;
}
printf("%I64d\n", ans);
}
}