思路：
动态开点线段树，在值域范围很大的时候可以采用此方法。这里维护了区间最大值和区间赋值。
实现：
1 class SegmentTree { 2 public: 3 int N = (int)1e9; 4 class Node { 5 public: 6 // ls 和 rs 分别代表当前区间的左右子节点 7 Node*ls=nullptr, *rs=nullptr; 8 // val 代表当前区间的最大高度，add 为懒标记 9 int val=0, add=0; 10 Node(){} 11 }; 12 Node*root = nullptr; 13 SegmentTree(int n){ 14 root=new Node(); 15 N=n; 16 } 17 void update(int l,int r,int v){ 18 _update(root,0,N,l,r,v); 19 } 20 void _update(Node*node, int lc, int rc, int l, int r, int v) { 21 if (l <= lc && rc <= r) { 22 node->add = v; 23 node->val = v; 24 return ; 25 } 26 pushdown(node); 27 int mid = lc + rc >> 1; 28 if (l <= mid) _update(node->ls, lc, mid, l, r, v); 29 if (r > mid) _update(node->rs, mid + 1, rc, l, r, v); 30 pushup(node); 31 } 32 int query(int l,int r){ 33 return _query(root,0,N,l,r); 34 } 35 int _query(Node*node, int lc, int rc, int l, int r) { 36 if (l <= lc && rc <= r) return node->val; 37 pushdown(node); 38 int mid = lc + rc >> 1, ans = 0; 39 if (l <= mid) ans = _query(node->ls, lc, mid, l, r); 40 if (r > mid) ans = max(ans, _query(node->rs, mid + 1, rc, l, r)); 41 return ans; 42 } 43 void pushdown(Node*node) { 44 if (node->ls == nullptr) node->ls = new Node(); 45 if (node->rs == nullptr) node->rs = new Node(); 46 if (node->add == 0) return ; 47 node->ls->add = node->add; node->rs->add = node->add; 48 node->ls->val = node->add; node->rs->val = node->add; 49 node->add = 0; 50 } 51 void pushup(Node*node) { 52 node->val = max(node->ls->val, node->rs->val); 53 } 54 55 }; 56 class Solution { 57 public: 58 vector<int>fallingSquares(vector<vector<int>>&ps) { 59 vector<int>res; 60 int N=1e9; 61 SegmentTree*st=new SegmentTree(N); 62 for (auto&info:ps) { 63 int x=info[0],h=info[1],cur=st->query(x,x+h-1); 64 st->update(x,x+h-1,cur+h); 65 res.push_back(st->query(0,N)); 66 } 67 return res; 68 } 69 };