leetcode之Range Sum Query - Immutable

题目：

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.
解答：
由于求和具有连续性，直接记录到当前位置的和，然后直接减即可
只是题目的ｔａｇ是ｄｐ，可是我并没有看出ｄｐ体现在哪，难道是ｓｕｍ［ｉ］　＝　ｓｕｍ［ｉ　－　１］＋　ｎｕｍ［ｉ］这？

class NumArray {
public:
NumArray(vector<int> &nums) {
tmp = nums;
int cnt = 0;
int size = nums.size();
dp = new int[size + 1];
dp[0] = 0;
for(int i = 0;i < nums.size();++i)
{
dp[i + 1] = dp[i] + nums[i];
}
}

int sumRange(int i, int j) {
return (dp[j + 1] - dp[i + 1] + tmp[i]);
}
private:
vector<int> tmp;
int *dp;
};