RT，调了 0.5h 硬是什么都没看出来……

过了样例，WA 10pts

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
using namespace std;
inline int read(){
    int x = 0, f = 1; char ch = getchar();
    while(ch < '0' || ch > '9'){ if(ch == '-') f = -1; ch = getchar(); }
    while(ch >= '0' && ch <= '9'){ x = x * 10 + (ch ^ 48); ch = getchar(); }
    return x * f;
}
char s[20];
int n, m, len, ok[80], num[80], f[110][80][80], a[110], ans;
inline int num1(int x){
	int ans = 0;
	while(x){
		++ans;
		x &= x - 1;
	}
	return ans;
}
int main(){
	//freopen("P2704.in", "r", stdin);
	//freopen("P2704.out", "w", stdout);
	scanf("%d%d", &n, &m);
	for(int i = 1; i <= n; ++i){
		scanf("%s", s);
		for(int j = 0; j < m; ++j){
			a[i] = (a[i] << 1) + (s[j] == 'P');
		}
	}
	for(int i = 0; i < (1 << m); ++i)
		if(!(i & (i << 1)) && !(i & (i << 2)) && !(i & (i >> 1)) && !(i & (i >> 2)))
			ok[++len] = i, num[len] = num1(i);
	for(int i = 1; i <= len; ++i)
		if(ok[i] | a[1] == a[1])
			f[1][i][0] = num[i];
	for(int i = 1; i <= len; ++i)
		for(int j = 1; j <= len; ++j)
			if((ok[i] | a[2] == a[2]) && (ok[j] | a[1] == a[1]) && !(ok[i] & ok[j]))
				f[2][i][j] = num[i] + num[j];
	for(int i = 3; i <= n; ++i)
		for(int j = 1; j <= len; ++j)
			if(ok[j] | a[i] == a[i])
				for(int k = 1; k <= len; ++k)
					if((ok[k] | a[i - 1] == a[i - 1]) && !(ok[j] & ok[k]))
						for(int l = 1; l <= len; ++l)
							if((ok[l] | a[i - 2] == a[i - 2]) && !(ok[k] & ok[l]) && !(ok[j] & ok[l]))
								f[i][j][k] = max(f[i][j][k], f[i - 1][k][l] + num[j]);
	for(int i = 1; i <= len; ++i) for(int j = 1; j <= len; ++j) ans = max(ans, f[n][i][j]);
	printf("%d", ans);
	return 0;
}

如果是一些申必错误请 D 死这个彩笔。