Week 3 @ 2025 算法周记【前缀和 + 双指针数组】

type NumArray struct {
    sums []int
}


func Constructor(nums []int) NumArray {
    sums := make([]int, len(nums))
    sums[0] = nums[0]
    for i := 1; i < len(nums); i++ {
        sums[i] = sums[i-1] + nums[i]
    }
    return NumArray{sums}
}


func (this *NumArray) SumRange(left int, right int) int {
    if left == 0 {
        return this.sums[right] 
    }
    
    return this.sums[right] - this.sums[left-1]
}


/**
 * Your NumArray object will be instantiated and called as such:
 * obj := Constructor(nums);
 * param_1 := obj.SumRange(left,right);
 */