数组建 BST

#include <bits/stdc++.h>
using namespace std;

const int maxn = 1e5 + 10;
int N, root = 1;
int vis[maxn], dep[maxn];
vector<int> pre;
vector<int> lev[maxn];
int depth = -1;

struct Node{
    int val;
    int l;
    int r;
}node[maxn];

void order(int root) {
    if(!root) return;

    if(node[root].l != -1) order(node[root].l);
    if(node[root].r != -1) order(node[root].r);
    pre.push_back(node[root].val);
}

void levelorder(int root) {
    if(!root) return;
    queue<int> q;
    q.push(root);
    dep[root] = 1;
    while(!q.empty()) {
        int t = q.front();
        q.pop();

        lev[dep[t]].push_back(node[t].val);
        if(node[t].l != -1) q.push(node[t].l), dep[node[t].l] = dep[t] + 1, depth = max(depth, dep[node[t].l]);
        if(node[t].r != -1) q.push(node[t].r), dep[node[t].r] = dep[t] + 1, depth = max(depth, dep[node[t].r]);
    }
}

int main() {
    scanf("%d", &N);
    memset(vis, 0, sizeof(vis));
    memset(dep, 0, sizeof(dep));
    for(int i = 1; i <= N; i ++) {
        scanf("%d%d%d", &node[i].val, &node[i].l, &node[i].r);
        if(node[i].l != -1) vis[node[i].l] = 1;
        if(node[i].r != -1) vis[node[i].r] = 1;
    }

    while(vis[root]) root ++;

    levelorder(root);
    //printf("%d\n", depth);

    for(int i = 1; i <= depth; i ++) {
        if(i % 2 == 0) {
            for(int j = lev[i].size() - 1; j >= 0; j --)
                printf("%d ", lev[i][j]);
        } else {
            for(int j = 0; j < lev[i].size(); j ++)
                printf("%d ", lev[i][j]);
        }
        //printf("%d\n", lev[i].size());
    }
    //for(int i = 0; i < lev.size(); i ++)
        //printf("%d%s", lev[i], i != lev.size() - 1 ? " " : "\n");

    return 0;
}

----------------------------------------------------

#include <bits/stdc++.h>
using namespace std;

int N, root = 0;
int a[110];

struct Node{
    int val;
    int l = -1;
    int r = -1;
    int fa = -1;
    int lev = 0;
}node[110];

void BuildBST(int root, int x) {
    if(node[root].val > node[x].val) {
        if(node[root].l == -1) {
            node[root].l = x;
            node[x].fa = root;
            node[x].lev = node[root].lev + 1;
        } else BuildBST(node[root].l, x);
    } else if(node[root].val <= node[x].val) {
        if(node[root].r == -1) {
            node[root].r = x;
            node[x].fa = root;
            node[x].lev = node[root].lev + 1;
        } else BuildBST(node[root].r, x);
    }
}

int main() {
    scanf("%d", &N);
    for(int i = 0; i < N; i ++) {
        int x;
        scanf("%d", &x);
        node[i].val = x;
    }

    for(int i = 1; i < N; i ++)
        BuildBST(root, i);

    for(int i = 0; i < N; i ++)
        printf("%d %d %d %d %d\n", node[i].val, node[i].l, node[i].r, node[i].fa, node[i].lev);

    return 0;
}