Java 手打线段树，不是通用模板，后续写成模板吧。

代码是leetcode 218. The Skyline Problem.

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class Node {
    Node left;
    Node right;
    long l;
    long r;
    int flag = 0;
    int value = 0;

    Node(int x, long l, long r) {
        this.value = x;
        this.l = l;
        this.r = r;
    }

    void makeChildren() {
        if (this.l == this.r){
            return;
        }
        long m = (this.l + this.r)/2;
        if (this.left == null && this.l != this.r) {
            this.left = new Node(0, this.l, m);
        }
        if (this.right == null && this.l != this.r) {
            this.right = new Node(0,m+1, this.r);
        }
    }

    int get(int l, int r) {
        if (l < 0)
            return 0;

        //System.out.println(this.toString());
        if(l <= this.l && r >= this.r) {
            return this.value;
        }
        long m = (this.l + this.r) / 2;
        makeChildren();
        if (this.flag > 0) {
            this.left.value = Math.max(this.left.value, this.flag);
            this.right.value = Math.max(this.right.value, this.flag);
            this.left.flag = Math.max(this.left.flag, this.flag);
            this.right.flag = Math.max(this.right.flag, this.flag);
            this.flag = 0;
        }
        int max = 0;
        if (l <= m){
            //System.out.println(this.toString());
            max = Math.max(max, this.left.get(l, r));
        }
        if (r > m){
            max = Math.max(max, this.right.get(l, r));
        }
        return max;
    }

    void update(long l, long r, int value) {
        //System.out.println("update:" + this.toString());
        if (l <= this.l && r >= this.r) {
            this.value = Math.max(this.value, value);
            this.flag = Math.max(this.flag, value);
        } else {
            long m = (this.l + this.r)/2;
            makeChildren();

            if(this.flag > 0 && this.l != this.r) {
                this.left.value = Math.max(this.left.value, this.flag);
                this.right.value = Math.max(this.right.value, this.flag);
                this.left.flag = Math.max(this.left.flag, this.flag);
                this.right.flag = Math.max(this.right.flag, this.flag);
                this.flag = 0;
            }

            if (l <= m){
                this.left.update(l, r, Math.max(this.flag, value));
            }
            if (r > m){
                this.right.update(l, r, Math.max(this.flag, value));
            }
            
            this.value = Math.max(this.left.value, this.right.value);
        }
    }

    @Override
    public String toString(){
        return String.format("[%d,%d]:%d,%d", this.l, this.r, this.value, this.flag);
    }
}
class Solution {
public static List<List<Integer>> getSkyline(int[][] buildings) {
        Node root = new Node(0, 0, Integer.MAX_VALUE);
        
        for(int[] building: buildings){
            root.update(building[0]+1, building[1], building[2]);
        }
        // for (int i = 0; i < 25; i++) {
        //     System.out.println(i+"\t"+root.get(i,i));
        // }   

        //"[[2,10],[3,15],[7,12],[12,0],[15,10],[20,8],[24,0]]"
        List<List<Integer>> ret = new ArrayList<>();
        Map<Integer, Integer> history = new HashMap<>();
        for(int[] building: buildings){
            history.put(building[0], root.get(building[0],building[0]));
            history.put(building[0] + 1, root.get(building[0] + 1,building[0] + 1));
            history.put(building[1], root.get(building[1],building[1]));
            history.put(building[1] + 1, root.get(building[1] + 1,building[1] + 1));

            if(history.get(building[0]) < history.get(building[0]+1)) {
                List<Integer> list = new ArrayList<>();
                list.add(building[0]);
                list.add(history.get(building[0]+1));
                ret.add(list);
            }
            if(history.get(building[1]+1) < history.get(building[1])) {
                List<Integer> list = new ArrayList<>();
                list.add(building[1]);
                list.add(history.get(building[1]+1));
                ret.add(list);
            }
        }

        Collections.sort(ret, (x1,x2) -> x1.get(0) - x2.get(0));
        
        //System.out.println(history);
        //System.out.println(ret);

        // for (int i = 0; i < 25; i++) {
        //     System.out.println(i+"\t"+root.get(i,i));
        // }

        // Queue<Pair<Node, Integer>> queue = new LinkedList<>();
        // queue.offer(new Pair<>(root, 0));
        // Map<Integer, List<Node>> map = new HashMap<>();
        // while(!queue.isEmpty()){
        //     Pair<Node, Integer> p = queue.poll();
        //     map.computeIfAbsent(p.getValue(), k->new ArrayList<>()).add(p.getKey());
        //     if(p.getKey().left != null) {
        //         queue.offer(new Pair<>(p.getKey().left, p.getValue()+1));
        //     }
        //     if(p.getKey().right != null) {
        //         queue.offer(new Pair<>(p.getKey().right, p.getValue()+1));
        //     }
        // }

        // for (int i = 0; i < 100; i++) {
        //     if (!map.containsKey(i)){
        //         break;
        //     }
        //     for(Node n: map.get(i)){
        //         System.out.print(n.toString()+"\t");
        //     }
        //     System.out.println();
        // }
        List<List<Integer>> omitDuplicated = new ArrayList<>();
        omitDuplicated.add(ret.get(0));
        for (int i = 1; i < ret.size(); i++) {
            if(!ret.get(i).get(0).equals(ret.get(i-1).get(0)) || !ret.get(i).get(1).equals(ret.get(i-1).get(1))){
                omitDuplicated.add(ret.get(i));
            } 
        }

        return omitDuplicated;
    }
}