《Cracking the Coding Interview》——第18章：难题——题目5

2014-04-29 01:51

题目：你有一个文本文件，每行一个单词。给定两个单词，请找出这两个单词在文件中出现的其中一对位置，使得这两个位置的距离最短。

解法：我的思路是建立倒排索引，计算出所有单词出现的所有位置。下面代码只给出了两个索引的处理方法。倒排索引一般以链表的形式出现，通过顺序扫描两个链表，类似归并排序算法中的merge过程，就能够找出最短距离。请看代码。

代码：

// 18.5 Given a text file containing words, find the shortest distance between two words.
#include <algorithm>
#include <climits>
using namespace std;

struct ListNode {
    int val;
    ListNode *next;
    ListNode(int _val = 0): val(_val), next(nullptr) {};
};

class Solution {
public:
    int minDist(ListNode *head1, ListNode *head2)
    {
        // the two list records the forward indices of two word, i.e. their occurrence position.
        // For example, 1->4->5->nullptr means the word appears at 1st, 4th and 5th line.
        
        int min_dist = INT_MAX;
        ListNode *p1, *p2;
        
        p1 = head1;
        p2 = head2;
        while (p1 != nullptr && p2 != nullptr) {
            if (p1->val < p2->val) {
                min_dist = min(min_dist, p2->val - p1->val);
                p1 = p1->next;
            } else {
                min_dist = min(min_dist, p1->val - p2->val);
                p2 = p2->next;
            }
        }
        
        return min_dist;
    }
};