HDU 2859 DP (求最大对称子矩阵）

题意

给一个 $N * N$ 的字符串矩阵，求出最大对称子矩阵，对称轴从左下角​​​-->​​右上角

思路：

参考代码：

#include <cstdio>
#include <algorithm>
#include <iostream>
#include <vector>
#include <map>
#include <queue>
#include <set>
#include <cstring>
#include <cstdlib>
#include <math.h>
using namespace std;
typedef long long ll;
const int N = 1005;
const int maxn = 1e6 + 5;
ll a[maxn], b[maxn];
double x[N], y[N];
char s[N][N];
int dp[N][N];
int main()
{
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n;
  while (cin >> n && n)
  {
    memset(dp, 0, sizeof dp);
    memset(s, 0, sizeof s);
    for (int i = 1; i <= n; i++)
      cin >> (s[i] + 1);
    for (int i = 1; i <= n; i++)
      dp[i][n] = dp[1][i] = 1;
    int m = 1;
    for (int i = 1; i <= n; i++)
    {
      for (int j = 1; j <= n; j++)
      {
        if (i == 1 || j == n)
          continue;
        int x = i, y = j;
        while (x >= 1 && y <= n && s[x][j] == s[i][y])
          x--, y++;
        int ans = i - x;
        if (ans >= dp[i - 1][j + 1] + 1)
          dp[i][j] = dp[i - 1][j + 1] + 1;
        else
          dp[i][j] = ans;
        m = max(m, dp[i][j]);
      }
    }
    cout << m << endl;
  }
}