HDU4925-Apple Tree

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題意：n*m網格中種蘋果，每個網格要麼施肥，要麼種一個蘋果，每個種蘋果的格子，如果它的上下左右有各自有施肥的話，每有一個，蘋果數量*2，求怎麼種使得蘋果數量最多。

思路：交叉種植，即黑白染色法可得到最優解。注意特判當n=m=1時的情況。

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>using namespace std;const int MAXN = 105;int n, m;int g[MAXN][MAXN];int deal(int x, int y) {    int sum = 1;    if (g[x][y - 1] == 1)        sum *= 2;    if (g[x][y + 1] == 1)        sum *= 2;    if (g[x - 1][y] == 1)        sum *= 2;    if (g[x + 1][y] == 1)        sum *= 2;    return sum;}int main() {    int cas;    scanf("%d", &cas);    while (cas--) {        scanf("%d%d", &n, &m);                 if (n == 1 && m == 1) {            printf("1\n");             continue;         }        memset(g, 0, sizeof(g));        int flag = 1;        if (m % 2 == 1) {            for (int i = 1; i <= n; i++)                 for (int j = 1; j <= m; j++) {                    g[i][j] = flag;                     flag = -flag;                 }         }        else {            for (int i = 1; i <= n; i++) {                 for (int j = 1; j <= m; j++) {                    g[i][j] = flag;                     flag = -flag;                 }                flag = -flag;            }        }        long long ans = 0;        for (int i = 1; i <= n; i++)            for (int j = 1; j <= m; j++)                 if (g[i][j] == -1)                    ans += deal(i, j);         printf("%lld\n", ans);       }    return 0;}