leetcode刷题笔记307题 区域和检索

leetcode刷题笔记307题 区域和检索 - 数组可修改

源地址：307. 区域和检索 - 数组可修改

问题描述：

给定一个整数数组 nums，求出数组从索引 i 到 j (i ≤ j) 范围内元素的总和，包含 i, j 两点。

update(i, val) 函数可以通过将下标为 i 的数值更新为 val，从而对数列进行修改。

示例:

Given nums = [1, 3, 5]

sumRange(0, 2) -> 9
update(1, 2)
sumRange(0, 2) -> 8
说明:

数组仅可以在 update 函数下进行修改。
你可以假设 update 函数与 sumRange 函数的调用次数是均匀分布的。

//主要使用树状数组处理，树状数组详见https://www.cnblogs.com/xenny/p/9739600.html
//主要是构造三个函数 lowbit() query() add()
class NumArray(nums: Array[Int]) {
    val tr = Array.fill(nums.length+1)(0)
    val n = nums.length
    for (i <- 0 to n-1){
        add(i+1, nums(i))
         //println(tr.mkString(" "))
    }

    def lowbit(i: Int): Int = {
        return i & (-i)
    }

    def query(x: Int): Int = {
        var res = 0
        var i = x
        while (i > 0) {
            res += tr(i)
            i -= lowbit(i)
        }
        return res
    }

    def add(x: Int, v:Int): Unit = {
        var i = x
        while (i <= n) {
            tr(i) += v
            i += lowbit(i)
        }
    }

    def update(i: Int, value: Int) {
        add(i+1, value-nums(i))
        nums(i) = value
    }

    def sumRange(i: Int, j: Int): Int = {
        return query(j+1) - query(i)
    }

}

/**
 * Your NumArray object will be instantiated and called as such:
 * var obj = new NumArray(nums)
 * obj.update(i,`val`)
 * var param_2 = obj.sumRange(i,j)
 */

type NumArray struct {
    tr []int
    nums []int
}

func lowbit(x int) int {
    return x&(-x)
}

func (this *NumArray) Query(x int) int {
    res := 0
    for i := x; i > 0; i -= lowbit(i) {
        res += this.tr[i]
    }
    return res
}

func (this *NumArray) Add(x int, val int) {
    for i := x; i <= len(this.nums); i += lowbit(i){
        this.tr[i] += val
    }
}

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


func (this *NumArray) Update(i int, val int)  {
    this.Add(i+1, val-this.nums[i])
    this.nums[i] = val
}


func (this *NumArray) SumRange(i int, j int) int {
    return this.Query(j+1) - this.Query(i)
}


/**
 * Your NumArray object will be instantiated and called as such:
 * obj := Constructor(nums);
 * obj.Update(i,val);
 * param_2 := obj.SumRange(i,j);
 */