[BZOJ 3791] 作业 【DP】

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <algorithm>

using namespace std;

const int MaxN = 100000 + 5, MaxM = 100 + 5;

inline void Read(int &Num) {
	char c; c = getchar();
	while (c < ‘0‘ || c > ‘9‘) c = getchar();
	Num = c - ‘0‘; c = getchar();
	while (c >= ‘0‘ && c <= ‘9‘) {
		Num = Num * 10 + c - ‘0‘;
		c = getchar();
	}
}

inline int gmax(int a, int b) {return a > b ? a : b;}

int n, m, Ans;
int A[MaxN], f[3][MaxM][3];

int main() 
{
	Read(n); Read(m);
	for (int i = 1; i <= n; ++i) Read(A[i]);
	int Now = 0, Last = 1;
	m = m * 2 - 1;
	Ans = 0;
	for (int i = 1; i <= n; ++i) {
		for (int j = 1; j <= m; ++j) {
			f[Now][j][0] = gmax(f[Last][j][0], f[Last][j - 1][1]);
			f[Now][j][1] = gmax(f[Last][j][1], f[Last][j - 1][0]);
			if (A[i] == 0) ++f[Now][j][0];
			else ++f[Now][j][1];
			Ans = gmax(Ans, f[Now][j][0]);
			Ans = gmax(Ans, f[Now][j][1]);
		}
		Now ^= 1; Last ^= 1;
	}
	printf("%d\n", Ans);
	return 0;
}