poj2112

二分加网络流，开始虽然写了floyd，但是没有调用，导致错了许多次。

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
using namespace std;

#define N 300
#define inf 10000000

struct Edge
{
    int x, y, nxt;
    int c;
} bf[N * N];

int k, c, m, n, s, t;
int map[N][N];
int ne, head[N], cur[N], ps[N * N], dep[N];

void floyed()
{
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
            for (int k = 1; k <= n; k++)
                if (map[j][i] != inf && map[i][k] != inf)
                    if (map[j][i] + map[i][k] < map[j][k])
                        map[j][k] = map[j][i] + map[i][k];
}

void addedge(int x, int y, int c)
{
    bf[ne].x = x;
    bf[ne].y = y;
    bf[ne].c = c;
    bf[ne].nxt = head[x];
    head[x] = ne++;
    bf[ne].x = y;
    bf[ne].y = x;
    bf[ne].c = 0;
    bf[ne].nxt = head[y];
    head[y] = ne++;
}

int flow(int n, int s, int t)
{
    int tr, res = 0;
    int i, j, k, f, r, top;
    while (1)
    {
        memset(dep, -1, n * sizeof(int));
        for (f = dep[ps[0] = s] = 0, r = 1; f != r;)
            for (i = ps[f++], j = head[i]; j; j = bf[j].nxt)
            {
                if (bf[j].c && -1 == dep[k = bf[j].y])
                {
                    dep[k] = dep[i] + 1;
                    ps[r++] = k;
                    if (k == t)
                    {
                        f = r;
                        break;
                    }
                }
            }
        if (-1 == dep[t])
            break;
        memcpy(cur, head, n * sizeof(int));
        for (i = s, top = 0;;)
        {
            if ((i == t))
            {
                for (k = 0, tr = inf; k < top; ++k)
                    if (bf[ps[k]].c < tr)
                        tr = bf[ps[f = k]].c;
                for (k = 0; k < top; ++k)
                    bf[ps[k]].c -= tr, bf[ps[k] ^ 1].c += tr;
                res += tr;
                i = bf[ps[top = f]].x;
            }
            for (j = cur[i]; cur[i]; j = cur[i] = bf[cur[i]].nxt)
                if (bf[j].c && dep[i] + 1 == dep[bf[j].y])
                    break;
            if (cur[i])
            {
                ps[top++] = cur[i];
                i = bf[cur[i]].y;
            }
            else
            {
                if (0 == top)
                    break;
                dep[i] = -1;
                i = bf[ps[--top]].x;
            }
        }
    }
    return res;
}

bool ok(int d)
{
    ne = 2;
    memset(head, 0, sizeof(head));
    s = 0;
    t = n + 1;
    for (int i = 1; i <= k; i++)
        addedge(i, t, m);
    for (int i = k + 1; i <= n; i++)
        addedge(s, i, 1);
    for (int i = k + 1; i <= n; i++)
        for (int j = 1; j <= k; j++)
            if (map[i][j] <= d)
                addedge(i, j, 1);
    int ret = flow(n + 2, s, t);
    return (ret == c);
}

int binarysearch()
{
    int l = 0;
    int r = 20000;
    int mid;
    while (l < r)
    {
        mid = (l + r) / 2;
        if (ok(mid))
            r = mid;
        else
            l = mid + 1;
    }
    return l;
}

int main()
{
    //freopen("t.txt", "r", stdin);
    scanf("%d%d%d", &k, &c, &m);
    n = c + k;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
        {
            scanf("%d", &map[i][j]);
            if (map[i][j] == 0 && (i != j))
                map[i][j] = inf;
        }
    floyed();
    int ans = binarysearch();
    printf("%d\n", ans);
    return 0;
}