Leetcode: Range Sum Query – Immutable

Range Sum Query – Immutable



Similar Problems:


Given an integer array nums, find the sum of the elements between indices i and j (i <= j), inclusive.

Example:
Given nums = [-2, 0, 3, -5, 2, -1]

sumRange(0, 2) -> 1
sumRange(2, 5) -> -1
sumRange(0, 5) -> -3

Note:

  • You may assume that the array does not change.
  • There are many calls to sumRange function.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.


## Blog link: 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)
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