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2643. Row With Maximum Ones

Description

Given a m x n binary matrix mat, find the 0-indexed position of the row that contains the maximum count of ones, and the number of ones in that row.

In case there are multiple rows that have the maximum count of ones, the row with the smallest row number should be selected.

Return an array containing the index of the row, and the number of ones in it.

 

Example 1:

Input: mat = [[0,1],[1,0]]
Output: [0,1]
Explanation: Both rows have the same number of 1's. So we return the index of the smaller row, 0, and the maximum count of ones (1). So, the answer is [0,1].

Example 2:

Input: mat = [[0,0,0],[0,1,1]]
Output: [1,2]
Explanation: The row indexed 1 has the maximum count of ones (2). So we return its index, 1, and the count. So, the answer is [1,2].

Example 3:

Input: mat = [[0,0],[1,1],[0,0]]
Output: [1,2]
Explanation: The row indexed 1 has the maximum count of ones (2). So the answer is [1,2].

 

Constraints:

  • m == mat.length 
  • n == mat[i].length 
  • 1 <= m, n <= 100 
  • mat[i][j] is either 0 or 1.

Solutions

Solution 1: Simulation

We directly traverse the matrix, count the number of $1$s in each row, and update the maximum value and the corresponding row index. Note that if the number of $1$s in the current row is equal to the maximum value, we need to choose the row with the smaller index.

The time complexity is $O(m \times n)$, where $m$ and $n$ are the number of rows and columns of the matrix, respectively. The space complexity is $O(1)$.

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class Solution:
    def rowAndMaximumOnes(self, mat: List[List[int]]) -> List[int]:
        ans = [0, 0]
        for i, row in enumerate(mat):
            cnt = row.count(1)
            if ans[1] < cnt:
                ans = [i, cnt]
        return ans

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class Solution {
    public int[] rowAndMaximumOnes(int[][] mat) {
        int[] ans = new int[2];
        for (int i = 0; i < mat.length; ++i) {
            int cnt = 0;
            for (int x : mat[i]) {
                if (x == 1) {
                    ++cnt;
                }
            }
            if (ans[1] < cnt) {
                ans[0] = i;
                ans[1] = cnt;
            }
        }
        return ans;
    }
}

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class Solution {
public:
    vector<int> rowAndMaximumOnes(vector<vector<int>>& mat) {
        vector<int> ans(2);
        for (int i = 0; i < mat.size(); ++i) {
            int cnt = 0;
            for (auto& x : mat[i]) {
                cnt += x == 1;
            }
            if (ans[1] < cnt) {
                ans[0] = i;
                ans[1] = cnt;
            }
        }
        return ans;
    }
};

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func rowAndMaximumOnes(mat [][]int) []int {
    ans := make([]int, 2)
    for i, row := range mat {
        cnt := 0
        for _, x := range row {
            if x == 1 {
                cnt++
            }
        }
        if ans[1] < cnt {
            ans[0], ans[1] = i, cnt
        }
    }
    return ans
}

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function rowAndMaximumOnes(mat: number[][]): number[] {
    const ans: number[] = [0, 0];
    for (let i = 0; i < mat.length; ++i) {
        const cnt = mat[i].reduce((a, b) => a + b);
        if (ans[1] < cnt) {
            ans[0] = i;
            ans[1] = cnt;
        }
    }
    return ans;
}

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impl Solution {
    pub fn row_and_maximum_ones(mat: Vec<Vec<i32>>) -> Vec<i32> {
        let mut ans = vec![0, 0];

        for (i, row) in mat.iter().enumerate() {
            let cnt = row.iter().filter(|&v| *v == 1).count() as i32;
            if ans[1] < cnt {
                ans[0] = i as i32;
                ans[1] = cnt;
            }
        }

        ans
    }
}

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