LeetCode 303. Range Sum Query - Immutable

303. Range Sum Query - Immutable

Description

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.

Analysis

这道题的意思其实就是求所给数组在所给区间内的数值和。

由于题目给出来的是两个函数。

所以我的做法是先设置一个向量，然后利用这个向量来记录从数组开始到当前位置i的数值和。

最后在sumRange中来求出结果数值和。

Code

class NumArray {
public:
vector<int> vec;

NumArray(vector<int> nums) {
if(nums.empty()) return ;

//for(int i = 0 ; i < nums.size();++i) vec.push_back(nums[i]);
vec.push_back(nums[0]);
for(int i = 1 ; i < nums.size(); ++i){
vec.push_back(nums[i]+vec[i-1]) ;
}
}

int sumRange(int i, int j) {
if(i == 0) return vec[j];
else return vec[j] - vec[i-1];
}
};

/**
* Your NumArray object will be instantiated and called as such:
* NumArray obj = new NumArray(nums);
* int param_1 = obj.sumRange(i,j);
*/