2931. Maximum Spending After Buying Items

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2931. Maximum Spending After Buying Items

Description

You are given a 0-indexed m * n integer matrix values, representing the values of m * n different items in m different shops. Each shop has n items where the j^th item in the i^th shop has a value of values[i][j]. Additionally, the items in the i^th shop are sorted in non-increasing order of value. That is, values[i][j] >= values[i][j + 1] for all 0 <= j < n - 1.

On each day, you would like to buy a single item from one of the shops. Specifically, On the d^th day you can:

  • Pick any shop i.
  • Buy the rightmost available item j for the price of values[i][j] * d. That is, find the greatest index j such that item j was never bought before, and buy it for the price of values[i][j] * d.

Note that all items are pairwise different. For example, if you have bought item 0 from shop 1, you can still buy item 0 from any other shop.

Return the maximum amount of money that can be spent on buying all m * n products.

Example 1:

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Input: values = [[8,5,2],[6,4,1],[9,7,3]]
Output: 285
Explanation: On the first day, we buy product 2 from shop 1 for a price of values[1][2] * 1 = 1.
On the second day, we buy product 2 from shop 0 for a price of values[0][2] * 2 = 4.
On the third day, we buy product 2 from shop 2 for a price of values[2][2] * 3 = 9.
On the fourth day, we buy product 1 from shop 1 for a price of values[1][1] * 4 = 16.
On the fifth day, we buy product 1 from shop 0 for a price of values[0][1] * 5 = 25.
On the sixth day, we buy product 0 from shop 1 for a price of values[1][0] * 6 = 36.
On the seventh day, we buy product 1 from shop 2 for a price of values[2][1] * 7 = 49.
On the eighth day, we buy product 0 from shop 0 for a price of values[0][0] * 8 = 64.
On the ninth day, we buy product 0 from shop 2 for a price of values[2][0] * 9 = 81.
Hence, our total spending is equal to 285.
It can be shown that 285 is the maximum amount of money that can be spent buying all m * n products.

Example 2:

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Input: values = [[10,8,6,4,2],[9,7,5,3,2]]
Output: 386
Explanation: On the first day, we buy product 4 from shop 0 for a price of values[0][4] * 1 = 2.
On the second day, we buy product 4 from shop 1 for a price of values[1][4] * 2 = 4.
On the third day, we buy product 3 from shop 1 for a price of values[1][3] * 3 = 9.
On the fourth day, we buy product 3 from shop 0 for a price of values[0][3] * 4 = 16.
On the fifth day, we buy product 2 from shop 1 for a price of values[1][2] * 5 = 25.
On the sixth day, we buy product 2 from shop 0 for a price of values[0][2] * 6 = 36.
On the seventh day, we buy product 1 from shop 1 for a price of values[1][1] * 7 = 49.
On the eighth day, we buy product 1 from shop 0 for a price of values[0][1] * 8 = 64
On the ninth day, we buy product 0 from shop 1 for a price of values[1][0] * 9 = 81.
On the tenth day, we buy product 0 from shop 0 for a price of values[0][0] * 10 = 100.
Hence, our total spending is equal to 386.
It can be shown that 386 is the maximum amount of money that can be spent buying all m * n products.

Constraints:

  • 1 <= m == values.length <= 10
  • 1 <= n == values[i].length <= 10^4
  • 1 <= values[i][j] <= 10^6
  • values[i] are sorted in non-increasing order.

Hints/Notes

Solution

Language: C++

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class Solution {
public:
    long long maxSpending(vector<vector<int>>& values) {
        long long res = 0;
        int m = values.size(), n = values[0].size();
        priority_queue<vector<int>, vector<vector<int>>, greater<vector<int>>> pq;
        for (int i = 0; i < m; i++) {
            pq.push({values[i][n - 1], i, n - 1});
        }
        long cur_day = 1;
        while (!pq.empty()) {
            auto tri = pq.top();
            pq.pop();
            int val = tri[0], row = tri[1], col = tri[2];
            res += cur_day * val;
            if (col) {
                col--;
                pq.push({values[row][col], row, col});
            }
            cur_day++;
        }
        return res;
    }
};