leetcode 318: Maximum Product of Word Lengths

Given a string array words, find the maximum value of length(word[i]) * length(word[j]) where the two words do not share common letters. You may assume that each word will contain only lower case letters. If no such two words exist, return 0.

Example 1:

Given ["abcw", "baz", "foo", "bar", "xtfn", "abcdef"]
Return 16
The two words can be "abcw", "xtfn".

Example 2:

Given ["a", "ab", "abc", "d", "cd", "bcd", "abcd"]
Return 4
The two words can be "ab", "cd".

Example 3:

Given ["a", "aa", "aaa", "aaaa"]
Return 0
No such pair of words.

题意：求，不包含相同字符的两个string的最大长度积；

思路：

如何降低判断两string是否包含相同字符的开销？？？

用bit来表示string元素中a-z每个字符是否出现；

 1 class Solution {
 2 public:
 3     int maxProduct(vector<string>& words) {
 4         int len = words.size();
 5         if(len==0)
 6             return 0;
 7         vector<int> v(len,0);
 8         vector<int> l(len,0);
 9         for(int i=0;i<len;i++)
10         {
11             string tstr = words[i];
12             int tlen = tstr.length();
13             l[i] = tlen;
14             for(int j=0;j<tlen;j++)
15             {
16                 int ttmp = 1<<(tstr[j]-‘a‘);
17                 v[i] |= ttmp;
18             }
19         }
20
21         int ans = 0;
22         for(int i=0;i<len;i++)
23         {
24             for(int j=i+1;j<len;j++)
25             {
26                 int t2 = v[i]&v[j];
27                 if(t2!=0)
28                     continue;
29                 int tmp = l[i]*l[j];
30                 if(tmp>ans)
31                     ans = tmp;
32             }
33         }
34         return ans;
35     }
36 };