BUPT-homework/semester3/pset2/2-2-Traverse-Binary-Search-Tree.c

#include <stdio.h>
#include <stdlib.h>

typedef struct treeNode {
  int val;
  struct treeNode *l;
  struct treeNode *r;
} treeNode;

treeNode *newNode(int val) {
  treeNode *root = malloc(sizeof(treeNode));
  root->val = val;
  root->l = NULL;
  root->r = NULL;
  return root;
}

void insertTree(treeNode *root, int val) {
  // Only insert at leaf.
  treeNode *par;
  int isL;
  treeNode *ptr = root;
  while (ptr != NULL) {
    par = ptr;
    if (ptr->val < val) {
      ptr = ptr->r;
      isL = 0;
    } else {
      ptr = ptr->l;
      isL = 1;
    }
  }

  if (isL) {
    par->l = newNode(val);
  } else {
    par->r = newNode(val);
  }
}

void freeTree(treeNode *root) {
  if (root) {
    freeTree(root->l);
    freeTree(root->r);
    free(root);
  }
}

void preorderTraversal(treeNode *root) {
  if (root) {
    printf("%d,", root->val);
    preorderTraversal(root->l);
    preorderTraversal(root->r);
  }
}

int main(void) {
  int tmp;
  scanf("%d,", &tmp);
  treeNode *root = newNode(tmp);

  while (scanf("%d,", &tmp) != EOF) {
    insertTree(root, tmp);
  }

  preorderTraversal(root);

  freeTree(root);
  return 0;
}