java版本

class SnapshotArray {int id = 0;List<int[]>[] snapshots;public SnapshotArray(int length) {snapshots = new List[length];for (int i = 0; i < length; i++) {snapshots[i] = new ArrayList<int[]>();}}public void set(int index, int val) {snapshots[index].add(new int[]{id, val});}public int snap() {int curr = id;id++;return curr;}public int get(int index, int snap_id) {List<int[]> snaplist = snapshots[index];int low = -1, high = snaplist.size() - 1;while (low < high) {int mid = low + (high - low + 1) / 2;if (snaplist.get(mid)[0] <= snap_id) {low = mid;} else {high = mid - 1;}}return low >= 0 ? snaplist.get(low)[1] : 0;}}

c++版本

class SnapshotArray {
public:int snap_id=0;unordered_map<int,vector<pair<int,int>>> history;SnapshotArray(int length) {}void set(int index, int val) {history[index].emplace_back(snap_id,val);}int snap() {return snap_id++;}int get(int index, int snap_id) {auto &h = history[index];int l = 0, r = h.size()-1, mid,target = snap_id+1;while(l <= r){mid = l +((r-l)>>1);if(h[mid].first < target){l = mid+1;}else{r = mid-1;}}return l-1 >= 0 ? h[l-1].second:0;}
};