<LeetCode OJ> 303. Range Sum Query - Immutable

303. Range Sum Query - Immutable

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Question

Total Accepted: 14338 Total
Submissions: 59913 Difficulty: Easy

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.

分析：
技巧题,，申请数组先算出结果，计算时直接获取结果进行相加减即可

class NumArray {
public:
NumArray(vector<int> &nums)
{//因为会被大量调用，所以先把所有的和算出来
vec=nums;
int sum = 0;
for (int i = 0; i < nums.size(); i++)
{
sum += nums[i];
sumArray.push_back(sum);
}
}

int sumRange(int i, int j) {
int sumi=sumArray[i];
int sumj=sumArray[j];
return sumj-sumi+vec[i];
}
vector<int> vec;
vector<int> sumArray;
};

// Your NumArray object will be instantiated and called as such:
// NumArray numArray(nums);
// numArray.sumRange(0, 1);
// numArray.sumRange(1, 2);

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原文地址：http://blog.csdn.net/ebowtang/article/details/50354078

原作者博客：http://blog.csdn.net/ebowtang