树

int getmin(int l,int r){
int res=l;
for (int i = l; i <= r; i ++ ){
if(w[res]>w[i]){
res=i;
}
}
return res;
}
void dfs(int l,int r,int d){
if(l>r){//树的必备
return ;
}
int root=getmin(l,r);
level[d].push_back(w[root]);
dfs(l,root-1,d+1);
dfs(root+1,r,d+1);
}

笛卡树

https://www.acwing.com/problem/content/4282/

#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>

using namespace std;
const int N = 40;
int n;
int w[N];
vector<int>level[N];
int getmin(int l,int r){
    int res=l;
    for (int i = l; i <= r; i ++ ){
        if(w[res]>w[i]){
            res=i;
        }
    }
    return res;
}
void  dfs(int l,int r,int d){
    if(l>r){
        return ;
    }
    int root=getmin(l,r);
    level[d].push_back(w[root]);
    dfs(l,root-1,d+1);
    dfs(root+1,r,d+1);
}

int main()
{
    cin>>n;
    for (int i = 0; i < n; i ++ ){
        cin >> w[i];
    }
    dfs(0,n-1,0);
    for (int i = 0; level[i].size(); i ++ ){
        for (auto x:level[i]){
            cout << x<<" ";
        }
    }
    return 0;
}

bfs

void bfs(int root)
{
    int hh = 0, tt = 0;
    q[0] = root;
    while (hh <= tt)
    {
        int t = q[hh ++ ];//好处先放左子树还是吸纳放右子树目标倾西
        cout << w[t] << ' ';
        if (L[t] != -1) q[ ++ tt] = L[t];//l[t] 存的是t结点的左右子树的下标
        if (R[t] != -1) q[ ++ tt] = R[t];
    }
}