[HDU 4280]Island Transport[SAP]

题目链接:[HDU 4280]Island Transport[SAP]

题意分析:

最西边的岛屿给最东边的岛屿运输,问最大运输能力。

解题思路:

最西边源点,最东边汇点,建边就行。

个人感受:

这题之所以写题解是因为,我竟然把边开的和点一样多= =,然后交上去不是RE而是T。。。。改了各种板子我都质疑人生了= =,结果是边开小了!!!!!教训教训!!!!

具体代码如下:

#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define ll long long
#define pr(x) cout << #x << " = " << (x) << '\n';
using namespace std;

const int MAXN = 1e5 + 100;//点数的最大值
const int MAXM = 4e5 + 100;//边数的最大值
const int INF = 0x3f3f3f3f;

struct Edge{
    int to,next,cap,flow;
}edge[MAXM];//注意是MAXM

int 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()
{
    for (int kk, kase = scanf("%d", &kk); kase <= kk; ++kase) {
        init();
        int n, m;
        scanf("%d%d", &n, &m);
        int mi = MAXN, mx = -MAXN, s, t, x, y;
        for (int i = 1; i <= n; ++i) {
            scanf("%d%d", &x, &y);
            if (x > mx) {
                mx = x;
                t = i;
            }
            if (x < mi) {
                mi = x;
                s = i;
            }
        }

        int l, r, c;
        while (m --) {
            scanf("%d%d%d", &l, &r, &c);
            addedge(l, r, c, c);
        }
        printf("%d\n", sap(s, t, n + 1));
    }
    return 0;
}


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