题意：求/直线的对称矩阵最大多大

思路：DP 每个点就是了

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int MAXN = 1200;

int dp[MAXN][MAXN];
char str[MAXN][MAXN];
int n;

int main() {
	while (scanf("%d", &n) != EOF && n) {
		for (int i = 0; i < n; i++)
			scanf("%s", str[i]);
		int ans = 1;
		for (int i = 0; i < n; i++) 
			for (int j = 0; j < n; j++) {
				if (i == 0 || j == n-1) {
					dp[i][j] = 1;
					continue;
				}
				int cnt1 = i, cnt2 = j;
				while (cnt1 >= 0 && cnt2 < n && str[i][cnt2] == str[cnt1][j]) {
					cnt1--;
					cnt2++;
				}
				int cur = i-cnt1;
				if (cur >= dp[i-1][j+1]+1) 
					dp[i][j] = dp[i-1][j+1] + 1;
				else dp[i][j] = cur;
				ans = max(ans, dp[i][j]);	
			}
		printf("%d\n", ans);
	}
	return 0;
}