[Leetcode]Range Sum Query

Range Sum Query - Immutable
Total Accepted: 9791 Total Submissions: 40927 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.

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水题，一次AC

class NumArray {
public:
    NumArray(vector<int> &nums) {
        int len = nums.size();
        if(!len)    return;
        sumFront.resize(len + 1);
        sumFront.push_back(0);
        for(int i = 0;i <= len - 1;++ i){
            sumFront[i + 1] = sumFront[i] + nums[i];
        }
    }

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


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