863. 二叉树中所有距离为 K 的结点

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C代码：dfs

/*** struct TreeNode {*     int val;*     struct TreeNode *left;*     struct TreeNode *right;* };*/typedef struct {int key;struct TreeNode* node;UT_hash_handle hh;
} HashTable;HashTable* head;
int* ans;
int ansSize;void addToHash(int ikey, struct TreeNode* node) {HashTable* out = NULL;HASH_FIND_INT(head, &ikey, out); // 去找当前值的父节点if (out == NULL) {out = (HashTable*)malloc(sizeof(HashTable));out->key = ikey;out->node = node;  // 保存当前节点的父节点HASH_ADD_INT(head, key, out);} else {out->node = node;}
}void findParents(struct TreeNode* root) {if (root->left != NULL) {addToHash(root->left->val, root);findParents(root->left);}if (root->right != NULL) {addToHash(root->right->val, root);findParents(root->right);}
}struct TreeNode* query(int ikey) {HashTable* out = NULL;HASH_FIND_INT(head, &ikey, out);if (out == NULL) {return NULL;}return out->node;
}// 从target节点往3个方向搜索，确保3个方向的途经点不能再dfs回去！
void findAns(struct TreeNode* node, struct TreeNode* from, int depth, int k) {if (node == NULL) {return;}if (depth == k) {  // 前序处理ans[ansSize++] = node->val;return;}if (node->left != from) {  // 搜索左右子节点，from是途径过的上一个结点findAns(node->left, node, depth + 1, k);}if (node->right != from) {findAns(node->right, node, depth + 1, k);}if (query(node->val) != from) {  // 顺着父节点往上搜索，node的父节点不等于fromfindAns(query(node->val), node, depth + 1, k);}
}int* distanceK(struct TreeNode* root, struct TreeNode* target, int k, int* returnSize) {head = NULL;                      // target是个结点ans = (int*)malloc(sizeof(int) * 500);ansSize = 0;findParents(root);  // 从root出发 DFS，记录每个结点的父结点findAns(target, NULL, 0, k); // 从target出发 DFS，寻找所有深度为 k 的结点*returnSize = ansSize;return ans;
}