[POJ 1459]Power Network[最大流]

题目链接：[POJ 1459]Power Network[最大流]

题意分析：

电力网中有n个节点，np个发电站，nc个消费者，m条单向边。问：整个电力网的最大供电量是多少？

解题思路：

源点和np建立电力容量大小的边，nc和汇点建立电力消费大小的边，然后根据m条互相相连求最大流即可。

题目读入需要在scanf中的'('前添加空格，具体原因参见链接：HERE

个人感受：

啰嗦了一堆，就是最大流罢了。读入坑了点，不过我是被n个点坑的= =，原先把源点建立为np + nc + 1，WA了两发= =

具体代码如下：

#include<algorithm>#include<cctype>#include<cmath>#include<cstdio>#include<cstring>#include<iomanip>#include<iostream>#include<map>#include<queue>#include<set>#include<sstream>#include<stack>#include<string>#define ll long long#define pr(x) cout << #x << " = " << (x) << '\n';using namespace std;const int MAXN = 500;//点数的最大值const int MAXM = 5e4;//边数的最大值const int INF = 0x3f3f3f3f;struct Edge{    int to,next,cap,flow;}edge[MAXM];//注意是MAXMint tol;int head[MAXN];int gap[MAXN],dep[MAXN],cur[MAXN];void addedge(int u,int v,int w,int rw = 0){    edge[tol].to = v; edge[tol].cap = w; edge[tol].flow = 0;    edge[tol].next = head[u]; head[u] = tol++;    edge[tol].to = u; edge[tol].cap = rw; edge[tol].flow = 0;    edge[tol].next = head[v]; head[v] = tol++;}int Q[MAXN];void BFS(int start,int end){    memset(dep,-1,sizeof(dep));    memset(gap,0,sizeof(gap));    gap[0] = 1;    int front = 0, rear = 0;    dep[end] = 0;    Q[rear++] = end;    while(front != rear)    {        int u = Q[front++];        for(int i = head[u]; i != -1; i = edge[i].next)        {            int v = edge[i].to;            if(dep[v] != -1)continue;            Q[rear++] = v;            dep[v] = dep[u] + 1;            gap[dep[v]]++;        }    }}int S[MAXN];int sap(int start,int end,int N){    BFS(start,end);    memcpy(cur,head,sizeof(head));    int top = 0;    int u = start;    int ans = 0;    while(dep[start] < N)    {        if(u == end)        {            int Min = INF;            int inser;            for(int i = 0;i < top;i++)            if(Min > edge[S[i]].cap - edge[S[i]].flow)            {                Min = edge[S[i]].cap - edge[S[i]].flow;                inser = i;            }            for(int i = 0;i < top;i++)            {                edge[S[i]].flow += Min;                edge[S[i]^1].flow -= Min;            }            ans += Min;            top = inser;            u = edge[S[top]^1].to;            continue;        }        bool flag = false;        int v;        for(int i = cur[u]; i != -1; i = edge[i].next)        {            v = edge[i].to;            if(edge[i].cap - edge[i].flow && dep[v]+1 == dep[u])            {                flag = true;                cur[u] = i;                break;            }        }        if(flag)        {            S[top++] = cur[u];            u = v;            continue;        }        int Min = N;        for(int i = head[u]; i != -1; i = edge[i].next)            if(edge[i].cap - edge[i].flow && dep[edge[i].to] < Min)            {                Min = dep[edge[i].to];                cur[u] = i;            }        gap[dep[u]]--;        if(!gap[dep[u]]) return ans;        dep[u] = Min + 1;        gap[dep[u]]++;        if(u != start)u = edge[S[--top]^1].to;    }    return ans;}void init() {    tol = 0;    memset(head,-1,sizeof(head));}int main(){    int n, np, nc, m, u, v, x;    while (~scanf("%d%d%d%d", &n, &np, &nc, &m)) {        init();        int src = n + 1, des = n + 2;        for (int i = 0; i < m; ++i) {            scanf(" (%d,%d)%d", &u, &v, &x);            addedge(u, v, x);        }        for (int i = 0; i < np; ++i) {            scanf(" (%d)%d", &u, &x);            addedge(src, u, x);        }        for (int i = 0; i < nc; ++i) {            scanf(" (%d)%d", &u, &x);            addedge(u, des, x);        }        printf("%d\n", sap(src, des, des + 1));    }    return 0;}