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。
示例：
输入：["SnapshotArray","set","snap","set","get"]
[[3],[0,5],[],[0,6],[0,0]]
输出：[null,null,0,null,5]
解释：
SnapshotArray snapshotArr = new SnapshotArray(3); // 初始化一个长度为 3 的快照数组
snapshotArr.set(0,5); // 令 array[0] = 5
snapshotArr.snap(); // 获取快照，返回 snap_id = 0
snapshotArr.set(0,6);
snapshotArr.get(0,0); // 获取 snap_id = 0 的快照中 array[0] 的值，返回 5
提示：
1 <= length <= 50000- 题目最多进行
50000次set，snap，和get的调用 。 0 <= index < length0 <= snap_id <我们调用snap()的总次数0 <= val <= 10^9
维护一个数组，数组中的每个元素是一个列表，列表中存储的是每次设置的值以及对应的快照编号。
每次设置值时，将值和快照编号添加到对应索引的列表中。
每次获取值时，使用二分查找，找到对应位置第一个大于快照编号 snap_id 的值，然后返回前一个值即可。
时间复杂度上，设置值的时间复杂度为
class SnapshotArray:
def __init__(self, length: int):
self.idx = 0
self.arr = defaultdict(list)
def set(self, index: int, val: int) -> None:
self.arr[index].append((self.idx, val))
def snap(self) -> int:
self.idx += 1
return self.idx - 1
def get(self, index: int, snap_id: int) -> int:
vals = self.arr[index]
i = bisect_right(vals, (snap_id, inf)) - 1
return 0 if i < 0 else vals[i][1]
# Your SnapshotArray object will be instantiated and called as such:
# obj = SnapshotArray(length)
# obj.set(index,val)
# param_2 = obj.snap()
# param_3 = obj.get(index,snap_id)class SnapshotArray {
private List<int[]>[] arr;
private int idx;
public SnapshotArray(int length) {
arr = new List[length];
Arrays.setAll(arr, k -> new ArrayList<>());
}
public void set(int index, int val) {
arr[index].add(new int[] {idx, val});
}
public int snap() {
return idx++;
}
public int get(int index, int snap_id) {
var vals = arr[index];
int left = 0, right = vals.size();
while (left < right) {
int mid = (left + right) >> 1;
if (vals.get(mid)[0] > snap_id) {
right = mid;
} else {
left = mid + 1;
}
}
return left == 0 ? 0 : vals.get(left - 1)[1];
}
}
/**
* Your SnapshotArray object will be instantiated and called as such:
* SnapshotArray obj = new SnapshotArray(length);
* obj.set(index,val);
* int param_2 = obj.snap();
* int param_3 = obj.get(index,snap_id);
*/class SnapshotArray {
public:
SnapshotArray(int length) {
idx = 0;
arr = vector<vector<pair<int, int>>>(length);
}
void set(int index, int val) {
arr[index].push_back({idx, val});
}
int snap() {
return idx++;
}
int get(int index, int snap_id) {
auto& vals = arr[index];
int left = 0, right = vals.size();
while (left < right) {
int mid = (left + right) >> 1;
if (vals[mid].first > snap_id) {
right = mid;
} else {
left = mid + 1;
}
}
return left == 0 ? 0 : vals[left - 1].second;
}
private:
vector<vector<pair<int, int>>> arr;
int idx;
};
/**
* Your SnapshotArray object will be instantiated and called as such:
* SnapshotArray* obj = new SnapshotArray(length);
* obj->set(index,val);
* int param_2 = obj->snap();
* int param_3 = obj->get(index,snap_id);
*/type SnapshotArray struct {
idx int
arr [][]pair
}
func Constructor(length int) SnapshotArray {
return SnapshotArray{0, make([][]pair, length)}
}
func (this *SnapshotArray) Set(index int, val int) {
this.arr[index] = append(this.arr[index], pair{this.idx, val})
}
func (this *SnapshotArray) Snap() int {
this.idx++
return this.idx - 1
}
func (this *SnapshotArray) Get(index int, snap_id int) int {
vals := this.arr[index]
i := sort.Search(len(vals), func(i int) bool { return vals[i].i > snap_id })
if i == 0 {
return 0
}
return vals[i-1].v
}
type pair struct{ i, v int }
/**
* 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);
*/