今天继续刷LeetCode,第303题,求数组中一个区间的数和。
分析:
类似于动态规划,先计算前面累加的和,然后通过相减求区间和。
问题:
1、动态规划;
附上C++代码:
class NumArray {
public:
NumArray(vector<int>& nums) {
if(nums.empty())
return;
else
{
sum.push_back(nums[0]);
int len=nums.size();
for(int i=1;i<len;i++)
{
sum.push_back(nums[i]+sum[i-1]);
}
}
}
int sumRange(int i, int j) {
if(0==i)
return sum[j];
int len=sum.size();
if(i<0||i>=len||j<0||j>=len||i>j)
return 0;
return sum[j]-sum[i-1];
}
private:
vector<int> sum;
};
/**
* Your NumArray object will be instantiated and called as such:
* NumArray* obj = new NumArray(nums);
* int param_1 = obj->sumRange(i,j);
*/
附上 Python代码:
class NumArray:
def __init__(self, nums: List[int]):
self.dp=nums
for i in range(1,len(nums)):
self.dp[i]+=self.dp[i-1]
def sumRange(self, i: int, j: int) -> int:
if i==0:
return self.dp[j]
else:
return self.dp[j]-self.dp[i-1]
# Your NumArray object will be instantiated and called as such:
# obj = NumArray(nums)
# param_1 = obj.sumRange(i,j)