[Swift]LeetCode1072. 按列翻转得到最大值等行数 | Flip Columns For Maximum Number of Equal Rows

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Given a matrix consisting of 0s and 1s, we may choose any number of columns in the matrix and flip every cell in that column.  Flipping a cell changes the value of that cell from 0 to 1 or from 1 to 0.

Return the maximum number of rows that have all values equal after some number of flips.

Example 1:

Input: [[0,1],[1,1]]
Output: 1
Explanation: After flipping no values, 1 row has all values equal.

Example 2:

Input: [[0,1],[1,0]]
Output: 2
Explanation: After flipping values in the first column, both rows have equal values.

Example 3:

Input: [[0,0,0],[0,0,1],[1,1,0]]
Output: 2
Explanation: After flipping values in the first two columns, the last two rows have equal values.

Note:

1. 1 <= matrix.length <= 300
2. 1 <= matrix[i].length <= 300
3. All matrix[i].length's are equal
4. matrix[i][j] is 0 or 1

---

给定由若干 0 和 1 组成的矩阵 matrix，从中选出任意数量的列并翻转其上的 每个 单元格。翻转后，单元格的值从 0 变成 1，或者从 1 变为 0 。

返回经过一些翻转后，行上所有值都相等的最大行数。 

示例 1：

输入：[[0,1],[1,1]]
输出：1
解释：不进行翻转，有 1 行所有值都相等。

示例 2：

输入：[[0,1],[1,0]]
输出：2
解释：翻转第一列的值之后，这两行都由相等的值组成。

示例 3：

输入：[[0,0,0],[0,0,1],[1,1,0]]
输出：2
解释：翻转前两列的值之后，后两行由相等的值组成。 

提示：

1. 1 <= matrix.length <= 300
2. 1 <= matrix[i].length <= 300
3. 所有 matrix[i].length 都相等
4. matrix[i][j] 为 0 或 1

---

Runtime: 1508 ms

Memory Usage: 21.3 MB

class Solution {
    func maxEqualRowsAfterFlips(_ matrix: [[Int]]) -> Int {
        var map:[String:Int] = [String:Int]()
        for x in matrix
        {
            var s:String = String()
            let flag:Int = x[0]
            for i in 0..<x.count
            {
                if x[i] == flag
                {
                    s.append("1")
                }
                else
                {
                    s.append("0")
                }
            }
            map[s,default:0] += 1
        }
        var result:Int = 0
        for val in map.values
        {
            result = max(result,val)
        }
        return result
    }
}

---

1600ms 

class Solution {
    func maxEqualRowsAfterFlips(_ matrix: [[Int]]) -> Int {
        var patternCountMap = [Int:Int]()
        let mask = 1 << matrix[0].count - 1
        return matrix.reduce(0) {
            let pattern = $1.reduce(0) { $0 << 1 | $1 } & mask
            if patternCountMap[pattern] != nil {
                patternCountMap[pattern]! += 1
                patternCountMap[mask - pattern]! += 1
            } else {
                patternCountMap[pattern] = 1
                patternCountMap[mask - pattern] = 1
            }
            return max($0, patternCountMap[pattern]!)
        }
    }
}