leetcoce-range sum query

303. Range Sum Query - Immutable.py

class NumArray:

    def __init__(self, nums: List[int]):
        self._prefix_sum = [0 for _ in range(len(nums))]
        if len(nums) != 0:
            self._prefix_sum[0] = nums[0]
        for i in range(1, len(nums)):
             self._prefix_sum[i] =  self._prefix_sum[i-1] + nums[i]
        
    def sumRange(self, i: int, j: int) -> int:
        if i == 0:
            return self._prefix_sum[j]
        return self._prefix_sum[j] - self._prefix_sum[i-1]


# Your NumArray object will be instantiated and called as such:
# obj = NumArray(nums)
# param_1 = obj.sumRange(i,j)