Leetcode: Substring with Concatenation of All Words

Description:

You are given a string, S, and a list of words, L, that are all of the same length. Find all starting indices of substring(s) in S that is a concatenation of each word in L exactly once and without any intervening characters.

For example, given:
S: "barfoothefoobarman"
L: ["foo", "bar"]

You should return the indices: [0,9].
(order does not matter).

分析： 这道题目告诉我们一定要认真读题目！ 题目做了限制，会使得解题容易的多： 单词表中的words长度一样！ 

这样题目只要建立了哈希表，即可使用循环解决。 注意中间也有一些简单的trick,比如长度限制扫描范围等。

 1 class Solution {
 2 public:
 3     vector<int> findSubstring(string S, vector<string> &L) {
 4         vector<int> result;
 5         int nums = L.size();
 6         if(nums==0) return result;
 7         int wordsz = L[0].size();
 8         if(S.size()<(wordsz*nums)) return result;
 9         
10         unordered_map<string,int> dict,backup;
11         string target;
12         for(int i=0;i<nums;i++)
13             dict[L[i]]++;
14         backup =dict;
15         
16         for(int i=0;i<=S.size()-(wordsz*nums);i++)
17         {
18             int hitnum = 0;
19             for(int j =i;j!=i+wordsz*nums;j+=wordsz)
20             {
21                 target.assign(S.begin()+j,S.begin()+j+wordsz);
22                 auto p = dict.find(target);
23                 if(p!=dict.end() && p->second)
24                 {
25                     hitnum++;
26                     p->second--;
27                 }
28                 else{
29                     dict = backup;
30                     break;
31                 }
32                 if(hitnum == nums)
33                 {
34                     dict = backup;
35                     result.push_back(i);
36                     break;
37                 }
38             }
39             
40         }
41         return result;
42     }
43 };