[DP]303. Range Sum Query - Immutable

题目描述

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

一道水题，主要就是注意一下效率。用暴力解法是会time limit exception的。

class NumArray:

    def __init__(self, nums):
        """
        :type nums: List[int]
        """
        self.arr = nums
        for i in range(1,len(nums)):
            self.arr[i] += self.arr[i-1] 

    def sumRange(self, i, j):
        """
        :type i: int
        :type j: int
        :rtype: int   """
        if i==0:
            return self.arr[j]
        else:
            return self.arr[j] - self.arr[i-1]


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

没有什么需要解释和记录的地方。

之前刷题一直想着要让代码更简短，但是其实应该更追求效率。