LeetCode109 Convert Sorted List to Binary Search Tree

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详细见：leetcode.com/problems/convert-sorted-list-to-binary-search-tree

Java Solution: github

package leetcode;import java.util.ArrayList;import java.util.HashMap;/* * Given a singly linked list where elements are sorted in ascending order, *  convert it to a height balanced BST. */import tools.ListNode辅助.ListNode;import tools.TreeNode辅助.TreeNode;public class P109_ConvertSortedListtoBinarySearchTree {public static void main(String[] args) {ListNode head = tools.ListNode辅助.A_一维生成器(new int[] {1, 2, 3});TreeNode root = new Solution2().sortedListToBST(head);tools.TreeNode辅助.B_按层打印(root);}/* * TLE了，对时间的要求很高哪。 */static class Solution {    public TreeNode sortedListToBST(ListNode head) {    int len = 0;    ListNode cur = head;    while (cur != null) {    len ++;    cur = cur.next;    }    int[] nums = new int[len];    len = 0;    cur = head;    while (cur != null) {    nums[len] = cur.val;    len ++;    cur = cur.next;    }        return sortedArrayToBST(nums, 0, len - 1);    }private TreeNode sortedArrayToBST(int[] nums, int i, int j) {if (i > j) {return null;}if (i == j) {return new TreeNode(nums[i]);}int root_index = (i + j) / 2;TreeNode root = new TreeNode(nums[root_index]);root.left = sortedArrayToBST(nums, i, root_index - 1);root.right = sortedArrayToBST(nums, root_index + 1, j);return root;}}/* * 还是TLE，是不是rehash的锅 * 下一个方法采用ArrayList的吧 */static class Solution2 {HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();    public TreeNode sortedListToBST(ListNode head) {    int count = 0;    while (head != null) {    map.put(count ++, head.val);    head = head.next;    }    return zxwtry_generate(0, count - 1);    }private TreeNode zxwtry_generate(int i, int j) {if (i > j) {return null;}if (i == j) {return new TreeNode(map.get(i));}int mid = (i + j) / 2;TreeNode root = new TreeNode(map.get(mid));root.left = zxwtry_generate(i, mid - 1);root.right = zxwtry_generate(mid + 1, j);return root;}}/* * 艰难地AC了 * 3 ms */static class Solution3 {ArrayList<Integer> arr = new ArrayList<>();    public TreeNode sortedListToBST(ListNode head) {    while (head != null) {    arr.add(head.val);    head = head.next;    }    return sortedArrayToBST(0, arr.size() - 1);    }    private TreeNode sortedArrayToBST(int i, int j) {if (i > j) {return null;}if (i == j) {return new TreeNode(arr.get(i));}int root_index = (i + j) / 2;TreeNode root = new TreeNode(arr.get(root_index));root.left = sortedArrayToBST(i, root_index - 1);root.right = sortedArrayToBST(root_index + 1, j);return root;}}}

C Solution: github

/**/#include <stdio.h>#include <stdlib.h>struct ListNode {    int val;    struct ListNode *next;};struct TreeNode {    int val;    struct TreeNode *left;    struct TreeNode *right;};typedef struct ListNode sln;typedef struct ListNode * pln;typedef struct TreeNode stn;typedef struct TreeNode * ptn;ptn search(int* a, int ai, int aj) {    int am = (ai + aj + 1) / 2;    ptn n = NULL;    if (ai > aj) return NULL;    n = (ptn) malloc(sizeof(stn));    n->left = search(a, ai, am-1);    n->right = search(a, am+1, aj);    n->val = a[am];    return n;}ptn sortedListToBST(pln h) {    int hn = 0, *a = NULL, i = 0;    pln t = h;    ptn ans = NULL;    while (t != NULL) {        t = t->next;        hn ++;    }    a = (int*) malloc(sizeof(int) * hn);    t = h;    while (t != NULL) {        a[i] = t->val;        t = t->next;        i ++;    }    ans = search(a, 0, hn-1);    free(a);    return ans;}

Python Solution: github

#coding=utf-8'''    url: leetcode.com/problems/convert-sorted-list-to-binary-search-tree    @author:     zxwtry    @email:      zxwtry@qq.com    @date:       2017年4月29日    @details:    Solution: 256ms 86.37%'''class ListNode(object):    def __init__(self, x):        self.val = x        self.next = Noneclass TreeNode(object):    def __init__(self, x):        self.val = x        self.left = None        self.right = Noneclass Solution(object):    def search(self, n, ni, nj):        if ni > nj: return None        nm = (ni+nj) // 2        root = TreeNode(n[nm])        root.left = self.search(n, ni, nm-1)        root.right = self.search(n, nm+1, nj)        return root        def sortedListToBST(self, h):        """        :type h: ListNode        :rtype: TreeNode        """        n, l = h, []        while n != None:             l.append(n.val)            n = n.next        return self.search(l, 0, len(l)-1)

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