Range Query on a List - Google Top Interview Questions


Problem Statement :


Implement a data structure with the following methods:

RangeSum(int[] nums) constructs a new instance with the given nums.

total(int i, int j) returns the sum of integers from nums between [i, j). 
That is, nums[i] + nums[i + 1] + ... + nums[j - 1].
Constraints

n ≤ 100,000 where n is the length of nums

k ≤ 100,000 where k is the number of calls to total


Example 1

Input

methods = ["constructor", "total", "total"]

arguments = [[[1, 2, 5, 0, 3, 7]], [0, 3], [1, 5]]`

Output

[None, 8, 10]

Explanation

r = RangeSum([1,2,5,0,3,7])

r.total(0, 3) == 8 # sum([1, 2, 5])

r.total(1, 5) == 10 # sum([2, 5, 0, 3])


Solution :



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                        Solution in C++ :

class RangeSum {
    public:
    RangeSum(vector<int>& nums) {
        n = nums.size();
        sum.resize(n, 0);
        sum[0] = nums[0];
        for (int i = 1; i < n; ++i) {
            sum[i] = sum[i - 1] + nums[i];
        }
    }

    int total(int i, int j) {
        int range = INT_MIN;
        if (i >= 0 && j >= 1 && i < n && j <= n && i <= j) {
            int left = i > 0 ? sum[i - 1] : 0;
            int right = sum[j - 1];
            range = right - left;
        }
        return range;
    }

    private:
    vector<int> sum;
    int n;
};
                    

                        Solution in Java :

import java.util.*;

class RangeSum {
    int[] pf;
    public RangeSum(int[] nums) {
        pf = new int[nums.length];
        pf[0] = nums[0];
        for (int i = 1; i < nums.length; i++) {
            pf[i] = nums[i] + pf[i - 1];
        }
    }
    public int total(int i, int j) {
        return i == 0 ? pf[j - 1] : pf[j - 1] - pf[i - 1];
    }
}
                    

                        Solution in Python : 
                            
class RangeSum:
    def calculateprefixsum(self, vals):
        vals.insert(0, 0)
        for i in range(1, len(vals)):
            vals[i] += vals[i - 1]
        return vals

    def __init__(self, nums):
        self.nums = nums
        self.prefixsum = self.calculateprefixsum(nums)

    def total(self, i, j):
        return self.prefixsum[j] - self.prefixsum[i]
                    

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