leetcode303-Range Sum Query - Immutable

2851 단어 LeetCodedp
문제 설명:
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.
문제 해결:
class NumArray {
    vector<int> sum;
public:
    NumArray(vector<int> &nums) {
        if(nums.size()==0) return;
        sum = vector<int> (nums.size(), 0);//vector       
        sum[0]=nums[0];
        for(int i=1;i<nums.size();i++)
        {
            sum[i] = sum[i-1]+nums[i];//      
        }
    }

    int sumRange(int i, int j) {
        return (i==0)?sum[j]:sum[j]-sum[i-1];//  i~j     
    }
};


// 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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