题目:给定一个整数数组 nums,求出数组从索引 i 到 j (i ≤ j) 范围内元素的总和,包含 i, j 两点。
示例:
给定 nums = [-2, 0, 3, -5, 2, -1],求和函数为 sumRange()
sumRange(0, 2) -> 1
sumRange(2, 5) -> -1
sumRange(0, 5) -> -3
思路:维护一个与原数组等长的数组,数组中每一个元素的值为原数组中该位置之前(包括该位置)所有元素的和
代码:
class NumArray(object):
def __init__(self, nums):
"""
:type nums: List[int]
"""
self.lst = []
tmp = 0
for i in range(len(nums)):
tmp += nums[i]
self.lst.append(tmp)
def sumRange(self, i, j):
"""
:type i: int
:type j: int
:rtype: int
"""
if i == 0:
return self.lst[j]
else:
return self.lst[j]-self.lst[i-1]
# Your NumArray object will be instantiated and called as such:
# obj = NumArray(nums)
# param_1 = obj.sumRange(i,j)