Leetcode: Range Sum Query – Immutable

// https://code.dennyzhang.com/range-sum-query-immutable
// Basic Ideas: presum
// Complexity: Time O(n), Space O(n)
type NumArray struct {
    l []int
}

func Constructor(nums []int) NumArray {
    //  add a dummy node to caculate nums[0...i]
    l := make([]int, len(nums)+1)
    for i, v := range nums{
        l[i+1] = l[i] + v
    }
    return NumArray{l:l}
}


func (this *NumArray) SumRange(i int, j int) int {
    return this.l[j+1]-this.l[i]
}

/**
 * Your NumArray object will be instantiated and called as such:
 * obj := Constructor(nums);
 * param_1 := obj.SumRange(i,j);
 */

## https://code.dennyzhang.com/range-sum-query-immutable
class NumArray(object):

    def __init__(self, nums):
        """
        :type nums: List[int]
        """
        length = len(nums)
        self._nums = nums
        self._sum = [0] * length
        sum_value = 0
        for i in range(0, length):
            sum_value += nums[i]
            self._sum[i] = sum_value

    def sumRange(self, i, j):
        """
        :type i: int
        :type j: int
        :rtype: int
        """
        return self._sum[j] - (self._sum[i-1] if i>0 else 0)
# Your NumArray object will be instantiated and called as such:
# obj = NumArray(nums)
# param_1 = obj.sumRange(i,j)