CodeForces 22b_Bargaining Table_dp(暴力)

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题目大意
给出一个01矩阵求其中矩形的最大周长
思路
暴力枚举矩形左上角顶点在其基础上枚举右下角
用pre维护前几行最早出现第一个1之前的位置

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <cmath>#define INF 0x3f3f3f3f#define rep0(i, n) for (int i = 0; i < n; i++)#define rep1(i, n) for (int i = 1; i <= n; i++)#define rep_0(i, n) for (int i = n - 1; i >= 0; i--)#define rep_1(i, n) for (int i = n; i > 0; i--)#define MAX(x, y) (((x) > (y)) ? (x) : (y))#define MIN(x, y) (((x) < (y)) ? (x) : (y))#define mem(x, y) memset(x, y, sizeof(x))#define MAXN 30char g[MAXN][MAXN];using namespace std;int main(){    #ifndef ONLINE_JUDGE        freopen("in.txt", "r", stdin);    #endif // ONLINE_JUDGE    int n, m;    //mem(dp, 0);    scanf("%d %d", &n, &m);    rep0(i, n)        scanf("%s", g[i]);    int re = 0;    rep0(i, n)    {        rep0(j, m)        {            if (g[i][j] == '1')                continue;            int flag = 0;            int pre = INF;            for (int a = i; a < n; a++)            {                if (flag)                    break;                for (int b = j; b < m; b++)                {                    if (g[a][b] == '1' && b == j)                    {                        flag = 1;                        //pre = -1;                        break;                    }                    else if (g[a][b] == '1')                    {                        pre = MIN(b - 1, pre);                        break;                    }                    if (b > pre)                        re = MAX(re, 2 + 2 * (b - j + 1));                    else                        re = MAX(re, (a > i) ? 2 * (b - j + 1 + a - i + 1) : (2 + 2 * (b - j + 1)));                }            }        }    }    printf("%d\n", re);    return 0;}

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