[LeetCode] 2500. Delete Greatest Value in Each Row

2500. Delete Greatest Value in Each Row

• Hardness: \(\color{green}\textsf{Easy}\)
• Ralated Topics: Array、Hash Table、Binary Search、Dynamic Programming、Sorting
• \(\color{blue}\textsf{Weekly Contest 323}\)

一、題目

You are given an m x n matrix grid consisting of positive integers.
Perform the following operation until grid becomes empty:

• Delete the element with the greatest value from each row. If multiple such elements exist, delete any of them.
• Add the maximum of deleted elements to the answer.
  Note that the number of columns decreases by one after each operation.
  Return the answer after performing the operations described above.

Example 1:

• Input: grid = [[1,2,4],[3,3,1]]
• Output: 8
• Explanation: The diagram above shows the removed values in each step.

• In the first operation, we remove 4 from the first row and 3 from the second row (notice that, there are two cells with value 3 and we can remove any of them). We add 4 to the answer.
• In the second operation, we remove 2 from the first row and 3 from the second row. We add 3 to the answer.
• In the third operation, we remove 1 from the first row and 1 from the second row. We add 1 to the answer.
  The final answer = 4 + 3 + 1 = 8.

Example 2:

• Input: grid = [[10]]
• Output: 10
• Explanation: The diagram above shows the removed values in each step.

• In the first operation, we remove 10 from the first row. We add 10 to the answer. The final answer = 10.

Constraints:

• m == grid.length
• n == grid[i].length
• 1 <= m, n <= 50
• 1 <= grid[i][j] <= 100

二、分析

• 將每一列的 vector 都各自排序後，依題意將每一欄取最大值並累加起來。

三、解題

1. Sort

• Time complexity: \(O(m\times n\log n)\)
• Space complexity: \(O(1)\)

int deleteGreatestValue(vector<vector<int>>& grid) {
    for (int i = 0; i < grid.size(); i++) {
        auto& row = grid[i];
        sort(row.begin(), row.end());
    }
    int res = 0;
    for (int j = 0; j < grid[0].size(); j++) {
        int tmp = 0;
        for (int i = 0; i < grid.size(); i++) {
            tmp = max(tmp, grid[i][j]);
        }
        res += tmp;
    }
    return res;
}

回目錄 Catalog