PAT A1135 Is It A Red Black Tree

判断一棵树是否是红黑树，按题给条件建树，dfs判断即可~

#include<bits/stdc++.h>
using namespace std;
const int maxn=1010;
struct node {
    int data;
    node * left=NULL;
    node * right=NULL;
};
void insert (node * &root,int x) {
    if (root==NULL) {
        root=new node;
        root->data=x;
        return;    
    }
    if (abs(x)<abs(root->data)) insert (root->left,x);
    else insert (root->right,x);
}
int getnum (node * root) {
    if (root==NULL) return 1;
    if (root->data>0)
    return max(getnum(root->left),getnum(root->right))+1;
    else return max(getnum(root->left),getnum(root->right));
}
int flag=0;
void dfs (node * root) {
    if (root==NULL) return;
    if (root->data<0&&root->left&&root->left->data<0) flag++;
    if (root->data<0&&root->right&&root->right->data<0) flag++;
    if (getnum(root->left)!=getnum(root->right)) flag++;
    dfs (root->left);
    dfs (root->right);
}
int main () {
    int T;
    scanf ("%d",&T);
    int N,x;
    while (T--) {
        node * root=NULL;
        scanf ("%d",&N);
        for (int i=0;i<N;i++) {
            scanf ("%d",&x);
            insert (root,x);
        }
        flag=0;
        if (root->data<0) flag++;
        dfs (root);
        if (flag==0) printf ("Yes
");
        else printf ("No
");
    }
    return 0;
}