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Formatted question description: https://leetcode.ca/all/1714.html

1714. Sum Of Special Evenly-Spaced Elements In Array

Level

Hard

Description

You are given a 0-indexed integer array nums consisting of n non-negative integers.

You are also given an array queries, where queries[i] = [x_i, y_i]. The answer to the i-th query is the sum of all nums[j] where x_i <= j < n and (j - x_i) is divisible by y_i.

Return an array answer where answer.length == queries.length and answer[i] is the answer to the i-th query modulo 10^9 + 7.

Example 1:

Input: nums = [0,1,2,3,4,5,6,7], queries = [[0,3],[5,1],[4,2]]

Output: [9,18,10]

Explanation: The answers of the queries are as follows:

1) The j indices that satisfy this query are 0, 3, and 6. nums[0] + nums[3] + nums[6] = 9

2) The j indices that satisfy this query are 5, 6, and 7. nums[5] + nums[6] + nums[7] = 18

3) The j indices that satisfy this query are 4 and 6. nums[4] + nums[6] = 10

Example 2:

Input: nums = [100,200,101,201,102,202,103,203], queries = [[0,7]]

Output: [303]

Constraints:

  • n == nums.length
  • 1 <= n <= 5 * 10^4
  • 0 <= nums[i] <= 10^9
  • 1 <= queries.length <= 1.5 * 10^5
  • 0 <= x_i < n
  • 1 <= y_i <= 5 * 10^4

Solution

Let n be the length of nums and let sqrt be the square root of n. Create a 2D array dp of n rows and sqrt - 1 columns, where dp[x][y] represents the query result of [x, y] when y is less than sqrt. For i from n - 1 to 0 and for j from 1 to sqrt - 1, if i + j < n, then dp[i][j] = nums[i] + dp[i + j][j]. Otherwise, dp[i][j] = nums[i].

For the i-th query [x, y], if y < sqrt, then answer[i] = dp[x][y]. Otherwise, calculate the sum accordingly and let answer[i] be the sum. Finally, return answer.

  • class Solution {
    public int[] solve(int[] nums, int[][] queries) {
        final int MODULO = 1000000007;
        int length = nums.length;
        int sqrt = (int) Math.sqrt(length);
        int queriesCount = queries.length;
        int[] answer = new int[queriesCount];
        long[][] dp = new long[length][sqrt];
        for (int i = length - 1; i >= 0; i--) {
            for (int j = 1; j < sqrt; j++) {
                if (i + j < length)
                    dp[i][j] = (nums[i] + dp[i + j][j]) % MODULO;
                else
                    dp[i][j] = nums[i];
            }
        }
        for (int i = 0; i < queriesCount; i++) {
            int x = queries[i][0], y = queries[i][1];
            if (y >= sqrt) {
                long sum = 0;
                while (x < length) {
                    sum = (sum + nums[x]) % MODULO;
                    x += y;
                }
                answer[i] = (int) sum;
            } else
                answer[i] = (int) dp[x][y];
        }
        return answer;
    }
}

  • class Solution {
public:
    vector<int> solve(vector<int>& nums, vector<vector<int>>& queries) {
        int n = nums.size();
        int m = (int) sqrt(n);
        const int mod = 1e9 + 7;
        int suf[m + 1][n + 1];
        memset(suf, 0, sizeof(suf));
        for (int i = 1; i <= m; ++i) {
            for (int j = n - 1; ~j; --j) {
                suf[i][j] = (suf[i][min(n, j + i)] + nums[j]) % mod;
            }
        }
        vector<int> ans;
        for (auto& q : queries) {
            int x = q[0], y = q[1];
            if (y <= m) {
                ans.push_back(suf[y][x]);
            } else {
                int s = 0;
                for (int i = x; i < n; i += y) {
                    s = (s + nums[i]) % mod;
                }
                ans.push_back(s);
            }
        }
        return ans;
    }
};

  • class Solution:
    def solve(self, nums: List[int], queries: List[List[int]]) -> List[int]:
        mod = 10**9 + 7
        n = len(nums)
        m = int(sqrt(n))
        suf = [[0] * (n + 1) for _ in range(m + 1)]
        for i in range(1, m + 1):
            for j in range(n - 1, -1, -1):
                suf[i][j] = suf[i][min(n, j + i)] + nums[j]
        ans = []
        for x, y in queries:
            if y <= m:
                ans.append(suf[y][x] % mod)
            else:
                ans.append(sum(nums[x::y]) % mod)
        return ans


  • func solve(nums []int, queries [][]int) (ans []int) {
	n := len(nums)
	m := int(math.Sqrt(float64(n)))
	const mod int = 1e9 + 7
	suf := make([][]int, m+1)
	for i := range suf {
		suf[i] = make([]int, n+1)
		for j := n - 1; j >= 0; j-- {
			suf[i][j] = (suf[i][min(n, j+i)] + nums[j]) % mod
		}
	}
	for _, q := range queries {
		x, y := q[0], q[1]
		if y <= m {
			ans = append(ans, suf[y][x])
		} else {
			s := 0
			for i := x; i < n; i += y {
				s = (s + nums[i]) % mod
			}
			ans = append(ans, s)
		}
	}
	return
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}

  • function solve(nums: number[], queries: number[][]): number[] {
    const n = nums.length;
    const m = Math.floor(Math.sqrt(n));
    const mod = 10 ** 9 + 7;
    const suf: number[][] = Array(m + 1)
        .fill(0)
        .map(() => Array(n + 1).fill(0));
    for (let i = 1; i <= m; ++i) {
        for (let j = n - 1; j >= 0; --j) {
            suf[i][j] = (suf[i][Math.min(n, j + i)] + nums[j]) % mod;
        }
    }
    const ans: number[] = [];
    for (const [x, y] of queries) {
        if (y <= m) {
            ans.push(suf[y][x]);
        } else {
            let s = 0;
            for (let i = x; i < n; i += y) {
                s = (s + nums[i]) % mod;
            }
            ans.push(s);
        }
    }
    return ans;
}

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