Leetcode 303. Range Sum Query -

文章作者：Tyan
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1. Description

Range Sum Query - Immutable

2. Solution

• Version 1

class NumArray {
public:
    NumArray(vector<int> nums) {
        this->nums = nums;
    }
    
    int sumRange(int i, int j) {
        int sum = 0;
        for(int index = i; index <= j; index++) {
            sum += nums[index];
        }
        return sum;
    }

private:
    vector<int> nums;
};

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

• Version 2

class NumArray {
public:
    NumArray(vector<int> nums) {
        int sum = 0;
        for(int num: nums) {
            sum += num;
            sums.push_back(sum);
        }
    }
    
    int sumRange(int i, int j) {
        if(i > 0) {
            return sums[j] - sums[i - 1];
        }
        return sums[j];
    }

private:
    vector<int> sums;
};

/**
 * Your NumArray object will be instantiated and called as such:
 * NumArray obj = new NumArray(nums);
 * int param_1 = obj.sumRange(i,j);
 */![Screen Shot 2019-02-18 at 17.21.44.png](https://img.haomeiwen.com/i3232548/929965674bc9107d.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)

Reference

1. https://leetcode.com/problems/range-sum-query-immutable/description/