2015-09-09 [一点资讯]--数据抓取和处理工程师--1面

时间：2015-09-09 10:00 ~ 11:00

地点：北京市海淀区王庄路1号 清华同方科技广场D座 西区 7层

1. 实现链表加法

链接：https://github.com/loverszhaokai/ALG/blob/master/src/add_long.cc

两次反转。

// Reverse a list
// E.g. 1->2->3 after reverse is: 3->2->1
static ListNode *reverse(ListNode *head)
{
    ListNode *pre_node = NULL, *next_node;

    while (head) {

        next_node = head->next;

        head->next = pre_node;

        pre_node = head;

        head = next_node;

    }

    return pre_node;
}

ListNode *add_long(ListNode *head1, ListNode *head2)
{
    if (head1 == NULL && head2 == NULL)
        return NULL;

    // Reverse head1 and head2
    head1 = reverse(head1);
    head2 = reverse(head2);

    ListNode *orig_head1 = head1;
    ListNode *orig_head2 = head2;

    ListNode pseudo_head(0); // pseudo_head.next is the real head
    ListNode *pre_node = &pseudo_head;
    ListNode *node;
    int carry = 0;

    while (head1 && head2) {

        carry += head1->val + head2->val;

        node = new ListNode(carry % 10);

        carry /= 10;
        pre_node->next = node;
        pre_node = node;

        head1 = head1->next;
        head2 = head2->next;
    }

    while (head1) {

        carry += head1->val;

        node = new ListNode(carry % 10);

        carry /= 10;
        pre_node->next = node;
        pre_node = node;

        head1 = head1->next;
    }

    while (head2) {

        carry += head2->val;

        node = new ListNode(carry % 10);

        carry /= 10;
        pre_node->next = node;
        pre_node = node;

        head2 = head2->next;
    }

    if (carry != 0) {

        node = new ListNode(carry % 10);
        pre_node->next = node;
    }

    // Reverse head1 and head2
    reverse(orig_head1);
    reverse(orig_head2);

    // pseudo_head.next is the real head
    return reverse(pseudo_head.next);
}

2. 查找最长非重复字符创的长度

#include <cmath>
#include <iostream>
#include <iomanip>
#include <string>

using namespace std;

// The string pstr points to only contain 0~9 and a~z
// Return the length of the longest non repeat characters
//
// E.g.
// pstr = aefgsasdw
//        ^    ^
// The longest non repeat characters is "aefgs", so it should return 5
//
int longest_non_repeat_characters(const char *pstr)
{
    int index[256];

    for (int iii = 0; iii < sizeof(index) / sizeof(int); iii++)
        index[iii] = -1;

    int ans = 0;
    int start = 0, cnt_pos = 0, end, len;

    const char *str = pstr;
    while (*str) {

        if (index[*str] != -1) {

            ans = max(ans, cnt_pos - start);

            end = index[*str];
            // Update start to end inclusive
            for (int iii = start; iii <= end; iii++)
                index[ pstr[iii] ] = -1;

            start = end + 1;

        }

        index[*str] = cnt_pos++;
        str++;
    }

    ans = max(ans, cnt_pos - start);

    return ans;
}

int main()
{
    const struct TestCase {
        const char *str;
        int ret;
    } test_cases[] = {
        { "", 0 },
        { "abc", 3 },
        { "abca", 3 },
        { "xyzafegsahkbacbst", 8 },
    };

    for (int iii = 0; iii < sizeof(test_cases) / sizeof(TestCase); iii++) {
        const TestCase &tc = test_cases[iii];

        if (tc.ret != longest_non_repeat_characters(tc.str)) {
            cout << "Case #" << iii << ": FAILED" <<  endl;
        }

    }

    return 0;
}