LeetCode探索之旅（79）-303Range sum

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)