BUPT-homework/semester3/pset2/2-1-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 printLevel(treeNode *root, int level, int *hasOutput) {
  if (root == NULL) {
    return;
  }
  if (level == 1) {
    *hasOutput = 1;
    printf("%d,", root->val);
  } else {
    printLevel(root->l, level - 1, hasOutput);
    printLevel(root->r, level - 1, hasOutput);
  }
}

int main(void) {
  int size;
  int level;
  scanf("%d", &size);

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

  for (int i = 1; i < size; i++) {
    scanf("%d,", &tmp);
    insertTree(root, tmp);
  }

  scanf("%d", &level);
  int *hasOutput = malloc(sizeof(int));
  *hasOutput = 0;
  printLevel(root, level, hasOutput);

  if (*hasOutput == 0) {
    printf("-1");
  }

  free(hasOutput);
  freeTree(root);
  return 0;
}