P1169 [ZJOI2007]棋盘制作

随手一写就冲进了最优解的第一页?

本来以为是dp, 但是经过仔细分析...这不就是二进制 + 单调栈么?

然后想正方形的情况...emm..好像正方形一定是最大矩形的子矩阵吧!

听说此题dp也可行?

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <stack>
using namespace std;
typedef pair<int, int> P;
const int MAXN = 2e3 + 20;
const int INF = 0x3f3f3f3f;
inline int read()
{
    int x = 0; char ch = getchar();
    while(!isdigit(ch)) ch = getchar();
    while(isdigit(ch)) x = x * 10 + ch - '0', ch = getchar();
    return x;
}

int N, M;
int sum[2][MAXN];
bool map[2][MAXN];
P ans(1, 1);

struct Sta
{
    stack<P> sta;
    
    void init(){
        pushin(0);
        while(!sta.empty()) sta.pop();
        return ;
    }

    void pushin(int h){
        if(sta.empty() || sta.top().first < h) {
            sta.push(P(h, 1));
            return ;
        }
        int len = 0, hei = INF;
        while(!sta.empty() && sta.top().first > h) {
            P p = sta.top(); sta.pop();
            len += p.second; hei = min(hei, p.first);
            
            ans.first = max(ans.first, len * p.first);
            ans.second = max(ans.second, min(len, hei) * min(len, hei));
        }
        sta.push(P(h, len + 1));
        return;
    }
}S;

int main()
{
    cin>>N>>M; int d = 0;
    
    for(int i = 1; i <= N; i++){
        d ^= 1;
        
        if(i == 1) {
            for(int j = 1; j <= M; j++) 
                sum[d][j] = 1, map[d][j] = read();
            continue;
        }
        for(int j = 1; j <= M; j++){
            map[d][j] = read();
            sum[d][j] = (map[d ^ 1][j] ^ map[d][j]) ? sum[d ^ 1][j] + 1 : 1;
            if(j - 1 && map[d][j] ^ map[d][j - 1]) S.pushin(sum[d][j]);
            else S.init(), S.pushin(sum[d][j]);
        }
        S.init();        
    }
    cout<<ans.second<<endl;
    cout<<ans.first<<endl;
    return 0;
}