Question

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

• Note:
  You may assume that the array does not change.
  There are many calls to sumRange function.

Solution

简单的动态规划，依次累加，table[j] - table[i - 1]就表示两者之间的求和，注意i - 1可能越界。

Code

class NumArray {public:    NumArray(vector
    
      nums) {        int total = 0;        for (int i = 0; i < nums.size(); i++) {            total += nums[i];            table.push_back(total);        }    }    int sumRange(int i, int j) {        return (table[j] - ((i - 1) < 0 ? 0 : table[i - 1]));    }private:    vector
     
       table;    };/** * Your NumArray object will be instantiated and called as such: * NumArray obj = new NumArray(nums); * int param_1 = obj.sumRange(i,j); */