HDU-3870-Catch the Theves

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ACM模版

描述

题解

用最小割做是要死人的，看了周冬前辈中学时的论文，搞清楚了这种题要转化为最短路搞，不过建起图来是一个恶心人的事情~~~

具体论文参见：浅析最大最小定理在信息学竞赛中的应用

代码

#include <iostream>#include <cstring>#include <vector>#include <queue>using namespace std;const int MAXN = 170000;const int INF = 0x3f3f3f3f;struct point{    int v, w;} Point;vector<point> Edge[MAXN];int n,S,T,q[MAXN];int dist[MAXN];bool inq[MAXN];int SPFA(){    int head = 0, tail = 0;    memset(inq, false, sizeof(inq));    for (int i = 0; i <= (n - 1) * (n - 1) + 1; i++)    {        dist[i] = INF;    }    q[tail++] = S;    dist[S] = 0;    inq[S] = true;    while (head != tail)    {        int k = q[head];        head = (head + 1) % MAXN;        inq[k] = false;        for (int i = 0; i < Edge[k].size(); i++)        {            Point = Edge[k][i];            if (dist[Point.v] > dist[k] + Point.w)            {                dist[Point.v] = dist[k] + Point.w;                if (!inq[Point.v])                {                    inq[Point.v] = true;                    q[tail] = Point.v;                    tail = (tail + 1) % MAXN;                }            }        }    }    return dist[T];}int main(){    int t;    scanf("%d", &t);    while (t--)    {        scanf("%d", &n);        for (int i = 0; i < (n - 1) * (n - 1) + 2; i++)        {            Edge[i].clear();        }        S = (n - 1) * (n - 1);        T = (n - 1) * (n - 1) + 1;        int w;        for (int i = 0; i < n; i++)        {            for (int j = 0; j < n; j++)            {                scanf("%d", &w);                Point.w = w;                if (i == 0 && j != n - 1)                {                    Point.v = j;                    Edge[S].push_back(Point);                }                else if (j == n - 1 && i != n - 1)                {                    Point.v = i * (n - 1) + j - 1;                    Edge[S].push_back(Point);                }                if (j == 0 && i != n - 1)                {                    Point.v = T;                    Edge[i * (n - 1)].push_back(Point);                }                else if (i == n - 1 && j != n - 1)                {                    Point.v = T;                    Edge[(n - 2) * (n - 1) + j].push_back(Point);                }                if (i != n - 1 && j != n - 1)                {                    if (i)                    {                        Point.v = (i - 1) * (n - 1) + j;                        Edge[i * (n - 1) + j].push_back(Point);                        Point.v = i * (n - 1) + j;                        Edge[(i - 1) * (n - 1) + j].push_back(Point);                    }                    if (j)                    {                        Point.v = i * (n - 1) + j - 1;                        Edge[i * (n - 1) + j].push_back(Point);                        Point.v = i * (n - 1) + j;                        Edge[i * (n - 1) + j - 1].push_back(Point);                    }                }            }        }        printf("%d\n", SPFA());    }    return 0;}

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