1146. 快照数组

题目：
实现支持下列接口的「快照数组」- SnapshotArray：

• SnapshotArray(int length) - 初始化一个与指定长度相等的 类数组 的数据结构。初始时，每个元素都等于 0。
• void set(index, val) - 会将指定索引 index 处的元素设置为 val。
• int snap() - 获取该数组的快照，并返回快照的编号 snap_id（快照号是调用 snap() 的总次数减去 1）。
• int get(index, snap_id) - 根据指定的 snap_id 选择快照，并返回该快照指定索引 index 的值。
  算法：
  方法一：数组

type SnapshotArray struct {
    Arr [][][]int
    SnapID int
}


func Constructor(length int) SnapshotArray {
    s := SnapshotArray{
        Arr: make([][][]int, length),
    }
    for i := range s.Arr {
        s.Arr[i] = make([][]int, 0)
    }
    return s
}


func (this *SnapshotArray) Set(index int, val int)  {
    this.Arr[index] = append(this.Arr[index], []int{this.SnapID, val})
}

// 执行这个命令snap才会+1
func (this *SnapshotArray) Snap() int {
    this.SnapID ++
    return  this.SnapID - 1
}


func (this *SnapshotArray) Get(index int, snap_id int) int {
    list := this.Arr[index]
    left, right := -1, len(list) - 1
    for left < right {
        mid := left + (right - left) / 2 + 1
        if list[mid][0] <= snap_id {
            left = mid
        } else {
            right = mid - 1
        }
    }
    // snap(),然后set，会导致snap_id=0时，list为空
    if left == -1 {
        return 0
    }
    return list[left][1]
}


/**
 * Your SnapshotArray object will be instantiated and called as such:
 * obj := Constructor(length);
 * obj.Set(index,val);
 * param_2 := obj.Snap();
 * param_3 := obj.Get(index,snap_id);
 */

方法二：初始化数组

type SnapshotArray struct {
    Arr [][][]int
    SnapID int
}


func Constructor(length int) SnapshotArray {
    s := SnapshotArray{
        Arr: make([][][]int, length),
    }
    for i := range s.Arr {
        s.Arr[i] = [][]int{[]int{0, 0}}
    }
    return s
}


func (this *SnapshotArray) Set(index int, val int)  {
    this.Arr[index] = append(this.Arr[index], []int{this.SnapID, val})
}

// 执行这个命令snap才会+1
func (this *SnapshotArray) Snap() int {
    this.SnapID ++
    return  this.SnapID - 1
}


func (this *SnapshotArray) Get(index int, snap_id int) int {
    list := this.Arr[index]
    left, right := 0, len(list) - 1
    for left < right {
        mid := (right + left) / 2 + 1
        if list[mid][0] <= snap_id {
            left = mid
        } else {
            right = mid - 1
        }
    }
    // // snap(),然后set，会导致snap_id=0时，list为空
    // if len(list[left]) == 0 {
    //     return 0
    // }
    return list[left][1]
}


/**
 * Your SnapshotArray object will be instantiated and called as such:
 * obj := Constructor(length);
 * obj.Set(index,val);
 * param_2 := obj.Snap();
 * param_3 := obj.Get(index,snap_id);
 */