Golang | Leetcode Golang题解之第307题区域和检索-数组可修改

题目：

题解：

type NumArray struct {
    nums, tree []int
}

func Constructor(nums []int) NumArray {
    tree := make([]int, len(nums)+1)
    na := NumArray{nums, tree}
    for i, num := range nums {
        na.add(i+1, num)
    }
    return na
}

func (na *NumArray) add(index, val int) {
    for ; index < len(na.tree); index += index & -index {
        na.tree[index] += val
    }
}

func (na *NumArray) prefixSum(index int) (sum int) {
    for ; index > 0; index &= index - 1 {
        sum += na.tree[index]
    }
    return
}

func (na *NumArray) Update(index, val int) {
    na.add(index+1, val-na.nums[index])
    na.nums[index] = val
}

func (na *NumArray) SumRange(left, right int) int {
    return na.prefixSum(right+1) - na.prefixSum(left)
}