303. Range Sum Query - Immutable(动态规划)

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

法一：暴力

 class NumArray {

 public:
     vector<int> Nums;

     NumArray(vector<int> nums) {
         Nums =nums;
     }

     int sumRange(int i, int j) {
         int res = ;
         for(int k = i;k<=j;k++)
             res+=Nums[k];
         return res;
     }
 };

法二：

sumRange(i,j)=sum[j+1]−sum[i]

 class NumArray {

 public:
     vector<int> Nums;
     vector<int> Sums;

     NumArray(vector<int> nums) {
         Nums =nums;
         Sums = vector<int>(nums.size()+,);
         for(int i = ;i<nums.size();i++)
             Sums[i+]=Sums[i]+nums[i];
     }

     int sumRange(int i, int j) {
         int res = ;
         res = Sums[j+]-Sums[i];
         return res;
     }
 };