2015-08-13 [百度]--实习开发测试工程师--1面

时间：2015-08-13  16:40 ~ 18:20

地点：北京市海淀区西北旺东路10号院  百度科技园1号楼

1. 问简历

。。。

2. 算法

只问了一道算法题目。

leetcode原题稍微改了下。

https://leetcode.com/problems/copy-list-with-random-pointer/

该题目的解法在这里 : https://github.com/loverszhaokai/leetcode/blob/master/138/sol_1S_NT.cc

题目：在线性链表的基础上，每一个节点都增加一个random指针，该random指针指向该节点或者该节点之后的节点。返回深拷贝。

解法1：

struct RandomListNode {
    int label;
    RandomListNode *next, *random;
    RandomListNode(int x) : label(x), next(NULL), random(NULL) {}
};

/**
 * Definition for singly-linked list with a random pointer.
 * struct RandomListNode {
 *     int label;
 *     RandomListNode *next, *random;
 *     RandomListNode(int x) : label(x), next(NULL), random(NULL) {}
 * };
 */
class Solution {
public:
    // Time  Complexcity: O(n^2)
    // Space Complexcity: O(n)
    RandomListNode *copyRandomList(RandomListNode *head) {
        list<RandomListNode *> random_nodes;

        if (!head)
            return NULL;

        RandomListNode *new_head = new RandomListNode(head->label);
        if (head->random == head) {
            new_head->random = new_head;
        } else {
            new_head->random = head->random;
            random_nodes.push_back(new_head->random);
        }

        RandomListNode *old_node = head->next;
        RandomListNode *new_node;
        RandomListNode *pre_node = new_head;

        while (old_node) {
            new_node = new RandomListNode(old_node->label);
            pre_node->next = new_node;
            pre_node = new_node;

            // Traverse random_nodes to find all the nodes whose random point to this node
            list<RandomListNode *>::iterator it = random_nodes.begin();
            while (it != random_nodes.end()) {
                if (*it == old_node) {
                    *it = new_node;
                    random_nodes.erase(it);
                } else 
                    it++;
            }

            if (old_node->random == old_node) {
                new_node->random = new_node;
            } else {
                new_node->random = old_node->random;
                random_nodes.push_back(new_node->random);
            }

            old_node = old_node->next;
        }
　　　　　return new_head;
    }
};

解法2：

/**
 * Definition for singly-linked list with a random pointer.
 * struct RandomListNode {
 *     int label;
 *     RandomListNode *next, *random;
 *     RandomListNode(int x) : label(x), next(NULL), random(NULL) {}
 * };
 */
class Solution {
public:
    // Time  Complexcity: O(n)
    // Space Complexcity: O(n)
    RandomListNode *copyRandomList(RandomListNode *head) {
        unordered_map<RandomListNode *, list<RandomListNode *> > parent_nodes;

        if (!head)
            return NULL;

        RandomListNode *new_head = new RandomListNode(head->label);
        if (head->random == head) {
            new_head->random = new_head;
        } else {
            parent_nodes[head->random].push_back(new_head);
        }

        RandomListNode *old_node = head->next;
        RandomListNode *new_node;
        RandomListNode *pre_node = new_head;

        while (old_node) {
            new_node = new RandomListNode(old_node->label);
            pre_node->next = new_node;
            pre_node = new_node;

            // Update the random pointer
            list<RandomListNode *> nodes = parent_nodes[old_node];
            list<RandomListNode *>::iterator it = nodes.begin();
            while (it != nodes.end()) {
                it->random = new_node;
                it++;
            }

            if (old_node->random == old_node) {
                new_node->random = new_node;
            } else {
                parent_nodes[old_node->random].push_back(new_node);
            }

            old_node = old_node->next;
        }
        return new_head;
    }
};

解法3：[面试官提示使用原来的链表，以达到O(1)的存储空间]  该方法不适合leetcode上的138题

struct RandomListNode {
    int label;
    RandomListNode *next, *random;
    RandomListNode(int x) : label(x), next(NULL), random(NULL) {}
};

/**
 * Definition for singly-linked list with a random pointer.
 * struct RandomListNode {
 *     int label;
 *     RandomListNode *next, *random;
 *     RandomListNode(int x) : label(x), next(NULL), random(NULL) {}
 * };
 */
class Solution {
public:
    // Time  Complexcity: O(n)
    // Space Complexcity: O(1)
    RandomListNode *copyRandomList(RandomListNode *head) {
        if (!head)
            return NULL;

        RandomListNode *new_head = new RandomListNode(head->label);
        RandomListNode *old_node = head;
        RandomListNode *new_node = new_head;
        RandomListNode *pre_node = new_head;
        RandomListNode *next_old_node;

        new_node->random = old_node;
        next_old_node = old_node->next;
        old_node->next = new_node;
        old_node = next_old_node;

        while (old_node) {
            new_node = new RandomListNode(old_node->label);
            pre_node->next = new_node;
            pre_node = new_node;

            new_node->random = old_node;
            next_old_node = old_node->next;
            old_node->next = new_node;
            old_node = next_old_node;
        }

        old_node = head;
        new_node = new_head;

        while (new_node) {
            old_node = new_node->random;
            new_node->random = old_node->random == NULL ? NULL : (old_node->random)->next;
            old_node->next = new_node->next == NULL ? NULL : (new_node->next)->random;

            new_node = new_node->next;
        }
        return new_head;
    }
};

3. 面试的实习职位，不会发校招offer，应该是88了。