hdu 1569 最大点权独立集

参考网上大牛的方法做的，A了，但做法的可行性我还没有想明白。慢慢再想吧，先贴代码~

/*
 * hdu1569/win.cpp
 * Created on: 2011-10-5
 * Author    : ben
 */
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <queue>
using namespace std;

typedef int typec;
const typec inf = 0x7fffffff;
const int MAXE = 40000;
const int MAXN = 3000;
typedef struct {
    int x, y, nxt;
    typec c;
} Edge;
Edge bf[MAXE];
int ne, head[MAXN], cur[MAXN], ps[MAXN], dep[MAXN];
int map[MAXN][MAXN];
typec sum;

inline void addedge(int x, int y, typec 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++;
}

typec flow(int n, int s, int t) {
    typec 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;
}

void init(int m, int n) {
    int s = m * n;
    int t = s + 1;
    typec value;
    sum = 0;
    for (int i = 0; i < m; i++) {
        for (int j = 0; j < n; j++) {
            scanf("%d", &value);
            sum += value;
            if ((i + j) % 2 == 0) {
                addedge(s, i * n + j, value);
                if (i > 0) {
                    addedge(i * n + j, (i - 1) * n + j, inf);
                }
                if (j > 0) {
                    addedge(i * n + j, i * n + j - 1, inf);
                }
                if (i < m - 1) {
                    addedge(i * n + j, (i + 1) * n + j, inf);
                }
                if (j < n - 1) {
                    addedge(i * n + j, i * n + j + 1, inf);
                }
            } else {
                addedge(i * n + j, t, value);
            }
        }
    }
}

int main() {
#ifndef ONLINE_JUDGE
    freopen("data.in", "r", stdin);
#endif
    int n, m;
    while (scanf("%d%d", &m, &n) != EOF) {
        ne = 2;
        memset(head, 0, sizeof(head));
        init(m, n);
        printf("%d\n", sum - flow(m * n + 2, m * n, m * n + 1));
    }
    return 0;
}