Leetcode: 85. 最大矩形(動態規劃+暴力)

description

給定一個僅包含 0 和 1 的二維二進制矩陣，找出只包含 1 的最大矩形，並返回其面積。

demonstration

輸入:
[
  ["1","0","1","0","0"],
  ["1","0","1","1","1"],
  ["1","1","1","1","1"],
  ["1","0","0","1","0"]
]
輸出: 6

來源：力扣（LeetCode）
鏈接：https://leetcode-cn.com/problems/maximal-rectangle
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class Solution {
public:
    int maximalRectangle(vector<vector<char>>& matrix) {
        int x = matrix.size();
        if (x == 0)
            return 0;
        int y = matrix[0].size();
        int dp[x][y];
        int maxarea = 0;
        memset(dp, 0, sizeof(dp));
        for (int i = 0; i < x; ++i) {
            for (int j = 0; j < y; ++j) {
                if (matrix[i][j] == '1') {
                    dp[i][j] = j == 0? 1 : dp[i][j-1] + 1;
                    int witdh = dp[i][j];
                    for (int k = i; k >= 0; --k) {
                        witdh = min(witdh, dp[k][j]);
                        maxarea = max(maxarea, witdh * (i - k + 1));
                    }
                }
            }
        }
        return maxarea;
    }
};

要點：

witdh = min(witdh, dp[k][j]);

此處取最小值，能保證進行面積計算時可使用的最大寬度