1043. Is It a Binary Search Tree (25)

#include<iostream>
#include<cstdlib>

//    6
//  5  7
//    6
//     6
using namespace std;

struct Node{
Node* left;
Node* right;
int value;
};

int a[1001];
int N;

Node* createTree(int first,int last){
if(last-first<0){
return NULL;
}
Node* root = (Node*)malloc(sizeof(Node));
root->value = a[first];
root->left = NULL;
root->right = NULL;
if(first == last){
//cout << root->value << endl;
return root;
}
int i = first+1;
if(a[i] < a[first]){
for(; i <= last;i++){
if(a[i] >= a[first]){
break;
}
}
//cout << i << endl;
root->left = createTree(first+1,i-1);
root->right = createTree(i,last);
}else{
for(; i <= last;i++){
if(a[i] < a[first]){
break;
}
}
//cout << i << endl;
root->right = createTree(first+1,i-1);
root->left = createTree(i,last);
}
//root->left = createTree(first+1,i-1);
//root->right = createTree(i,last);
return root;
}

bool first = true;
void visit(int value){
if(first == true){
cout << value;
first = false;
}else{
cout << ' ' << value ;
}
}

int pre1[1001];
int index1 = 0;
void preOrder1(Node* root){

pre1[index1++] = root->value;
if(root->left != NULL){
preOrder1(root->left);
}
if(root->right != NULL){
preOrder1(root->right);
}
}

int pre2[1001];
int index2 = 0;
void preOrder2(Node* root){

pre2[index2++] = root->value;
if(root->right != NULL){
preOrder2(root->right);
}
if(root->left != NULL){
preOrder2(root->left);
}
}

void postOrder1(Node* root){
if(root->left != NULL){
postOrder1(root->left);
}
if(root->right != NULL){
postOrder1(root->right);
}
visit(root->value);
}

void postOrder2(Node* root){
if(root->right != NULL){
postOrder2(root->right);
}if(root->left != NULL){
postOrder2(root->left);
}
visit(root->value);
}

int in1[1001];
int index3 = 0;
void inOrder1(Node* root){
if(root->left != NULL){
inOrder1(root->left);
}
in1[index3++] = root->value;
if(root->right != NULL){
inOrder1(root->right);
}
}

int in2[1001];
int index4 = 0;
void inOrder2(Node* root){
if(root->right != NULL){
inOrder2(root->right);
}
in2[index4++] = root->value;
if(root->left != NULL){
inOrder2(root->left);
}
}

bool isBST(Node* root){
inOrder1(root);
//cout << endl;
inOrder2(root);
//cout << endl;
bool isbst1 = true;
for(int i = 1 ; i < N;i++){
if(in1[i-1] > in1[i]){
isbst1 = false;
break;
}
}
bool isbst2 = true;
for(int i = 1 ; i < N;i++){
if(in2[i-1] > in2[i]){
isbst2 = false;
break;
}
}

return isbst1 || isbst2;
// return isbst1;
}

int main(){

cin >> N;

for(int i = 0;i < N;i++){
cin >> a[i];
}
Node* root = createTree(0,N-1);

if(!isBST(root)){
cout << "NO" << endl;
return 0;
}

bool flag1 = true;
bool flag2 = true;
preOrder1(root);
for(int i = 0; i < N;i++){
if(pre1[i] != a[i]){
flag1 = false;
break;
}
}
preOrder2(root);
for(int i = 0; i < N;i++){
if(pre2[i] != a[i]){
flag2 = false;
break;
}
}
if(flag1 == true){
cout << "YES" << endl;
postOrder1(root);
}else if(flag2 == true){
cout << "YES" << endl;
postOrder2(root);
}else{
cout << "NO" << endl;
}

return 0;
}

创建排序二叉树的第二种方式

<pre name="code" class="cpp">void insert(Node* &root, int value){if(root = null){root = new Node;root->value = value;root->left = root->right = NULL;return;}if(value < root->value){insert(root->left,value);}else{insert(root->right,value);}}