leetcode 303. Range Sum Query - Immutable（前缀和）

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.

前缀和的应用，很简单。

class NumArray {

public:

    int n;

    vector<int> s;

    NumArray(vector<int> &nums) {

        n = nums.size();

        if(n==)return;

        s.push_back(nums[]);

        for(int i=;i<n;i++){

            s.push_back(s.back()+nums[i]);

        }

    }

    int sumRange(int i, int j) {

        if(i>j)return ;

        if(i==) return s[j];

        return s[j]-s[i-];

    }

};

// Your NumArray object will be instantiated and called as such:

// NumArray numArray(nums);

// numArray.sumRange(0, 1);

// numArray.sumRange(1, 2);

巴特西

leetcode 303. Range Sum Query - Immutable（前缀和）

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