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-rw-r--r--all_possible_full_tree.c74
1 files changed, 74 insertions, 0 deletions
diff --git a/all_possible_full_tree.c b/all_possible_full_tree.c
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+++ b/all_possible_full_tree.c
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+// 894. All Possible Full Binary Trees
+#include <stdio.h>
+#include <stdlib.h>
+
+/*
+ * given an integer 'n', return a list of all possible full binary trees with
+ * 'n' nodes. each node of each tree in the answer must have 'node.val == 0'.
+ * each element of the answer is the root node of one possible tree. you may
+ * return the final list of trees in any order. a full binary tree is a binary
+ * tree where each node has exactly zero or two children
+ */
+
+struct TreeNode {
+ int val;
+ struct TreeNode *left;
+ struct TreeNode *right;
+};
+
+struct TreeNode **allPossibleFBT(int n, int *return_size) {
+ if (!n % 2) {
+ *return_size = 0;
+ return NULL;
+ }
+ if (n == 1) {
+ struct TreeNode *root = malloc(sizeof(struct TreeNode));
+ root->val = 0;
+ root->left = NULL;
+ root->right = NULL;
+ struct TreeNode **ans = malloc(sizeof(struct TreeNode *));
+ *return_size = 1;
+ ans[0] = root;
+ return ans;
+ }
+ if (n == 3) {
+ struct TreeNode *root = malloc(sizeof(struct TreeNode));
+ struct TreeNode *left = malloc(sizeof(struct TreeNode));
+ struct TreeNode *right = malloc(sizeof(struct TreeNode));
+ root->val = 0;
+ left->val = 0;
+ right->val = 0;
+ left->left = NULL;
+ left->right = NULL;
+ right->left = NULL;
+ right->right = NULL;
+ root->left = left;
+ root->right = right;
+ struct TreeNode **ans = malloc(sizeof(struct TreeNode));
+ *return_size = 1;
+ ans[0] = root;
+ return ans;
+ }
+ struct TreeNode **ans = malloc(5000 * sizeof(struct TreeNode));
+ int idx = 0;
+ for (int i = 1; i <= (n - 1); i += 2) {
+ int *cnt_l = calloc(1, sizeof(int));
+ int *cnt_r = calloc(1, sizeof(int));
+ struct TreeNode **l_tree = allPossibleFBT(i, cnt_l);
+ struct TreeNode **r_tree = allPossibleFBT(n - 1 - i, cnt_r);
+ for (int j = 0; j < (*cnt_l); j++) {
+ for (int k = 0; k < (*cnt_r); k++) {
+ struct TreeNode *new = malloc(sizeof(struct TreeNode));
+ new->val = 0;
+ new->left = l_tree[j];
+ new->right = r_tree[k];
+ ans[idx] = new;
+ idx++;
+ }
+ }
+ free(cnt_l), free(cnt_r);
+ }
+ ans = realloc(ans, idx * sizeof(struct TreeNode *));
+ *return_size = idx;
+ return ans;
+}