代码随想录算法训练营第23天 |530. 二叉搜索树的最小绝对差 | 501. 二叉搜索树中的众数

代码随想录算法训练营第23天 |530. 二叉搜索树的最小绝对差 | 501. 二叉搜索树中的众数 | 236. 二叉树的最近公共祖先

本文主要是介绍代码随想录算法训练营第23天 |530. 二叉搜索树的最小绝对差 | 501. 二叉搜索树中的众数 | 236. 二叉树的最近公共祖先，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

530. 二叉搜索树的最小绝对差

题目链接

解: 递归

/*** Definition for a binary tree node.* struct TreeNode {*     int val;*     struct TreeNode *left;*     struct TreeNode *right;* };*/void travel(struct TreeNode *node, int *array, int *idx) {if (node == NULL) return;travel(node->left, array, idx);array[(*idx)++] = node->val;travel(node->right, array, idx);
}int getMinimumDifference(struct TreeNode* root) {int array[10005] = {0};int idx = 0;travel(root, array, &idx);for (int i = 0; i < idx; i++) printf("%d\n", array[i]);int min = 0x3f3f3f;for (int i = 1; i < idx; i++) {if (array[i] - array[i-1] < min) {min = array[i] - array[i-1];}}return min;
}

解: 迭代

/*** Definition for a binary tree node.* struct TreeNode {*     int val;*     struct TreeNode *left;*     struct TreeNode *right;* };*/struct stack {int top;struct TreeNode *array[10005];
};int getMinimumDifference(struct TreeNode* root) {int min = 0x3f3f3f;struct TreeNode *pre = NULL, *node = root;struct stack *st = (struct stack *)malloc(sizeof(*st));memset(st, 0, sizeof(*st));st->top = -1;while (st->top != -1 || node != NULL) {while (node != NULL) {st->array[++st->top] = node;node = node->left;}node = st->array[st->top--];if (pre != NULL) {if (min > node->val - pre->val) {min = node->val - pre->val;}}pre = node;node = node->right;}return min;
}

501. 二叉搜索树中的众数

题目链接

解

/*** Definition for a binary tree node.* struct TreeNode {*     int val;*     struct TreeNode *left;*     struct TreeNode *right;* };*/
/*** Note: The returned array must be malloced, assume caller calls free().*/int cnt = 0;
int maxcnt = 0;
struct TreeNode *pre = NULL;
int *array = NULL;
int idx = 0;void travel(struct TreeNode *node) {if (node == NULL) return;travel(node->left);if (pre == NULL) {cnt = 1;} else if (pre->val == node->val) {cnt++;} else {cnt = 1;}pre = node;if (cnt == maxcnt) {array[idx++] = node->val;}if (cnt > maxcnt) {maxcnt = cnt;idx = 0;array[idx++] = node->val;}travel(node->right);
}int* findMode(struct TreeNode* root, int* returnSize) {cnt = maxcnt = idx = 0;pre = NULL;array = (int *)malloc(sizeof(int) *10005);memset(array, 0, sizeof(int) * 10005);*returnSize = 0;if (root == NULL) return array;travel(root);*returnSize = idx;return array;
}

leetcode中的全局变量并不是真正的全局变量, 每次都需要重置.

236. 二叉树的最近公共祖先

题目链接

解

/*** Definition for a binary tree node.* struct TreeNode {*     int val;*     struct TreeNode *left;*     struct TreeNode *right;* };*/
struct TreeNode* lowestCommonAncestor(struct TreeNode* root, struct TreeNode* p, struct TreeNode* q) {if (root == q || root == p || root == NULL) return root;struct TreeNode *left = lowestCommonAncestor(root->left, p, q);struct TreeNode *right = lowestCommonAncestor(root->right, p, q);if (left != NULL && right != NULL) return root;if (left != NULL && right == NULL) return left;else if (left == NULL && right != NULL) return right;else return NULL;
}