0221.md

• 动态规划，dp[i][j] 表示以 matrix[i][j] 为右下角的最大正方形边长

class Solution {
 public:
  int maximalSquare(vector<vector<char>>& matrix) {
    if (empty(matrix) || empty(matrix[0])) {
      return 0;
    }
    int res = 0;
    int m = size(matrix);
    int n = size(matrix[0]);
    vector<vector<int>> dp(m, vector<int>(n));
    for (int i = 0; i < m; ++i) {
      if (matrix[i][0] == '1') {
        dp[i][0] = 1;
        res = max(res, dp[i][0]);
      }
    }
    for (int i = 0; i < n; ++i) {
      if (matrix[0][i] == '1') {
        dp[0][i] = 1;
        res = max(res, dp[0][i]);
      }
    }
    for (int i = 1; i < m; ++i) {
      for (int j = 1; j < n; ++j) {
        if (matrix[i][j] == '1') {
          dp[i][j] = min({dp[i - 1][j - 1], dp[i - 1][j], dp[i][j - 1]}) + 1;
          res = max(res, dp[i][j]);
        }
      }
    }
    return res * res;
  }
};