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  • [Leetcode 54] 49 Anagrams

    Problem:

    Given an array of strings, return all groups of strings that are anagrams.

    Note: All inputs will be in lower-case.

    Analysis:

    anagrams are those strings that consist of same characters but in different order. A very simple way to solve the problem is try to find each string's anagrams. This requires O(n^2) by scanning through the string vector and comparing the two sorted string whether are the same. But it won't work if the geiven string vector is too big.

    A O(n) solution is as follows: use a map structure to keep the pair of <string, vector<string>>, the key is the sorted string the value is the original string's vector. In this way, we only need scan through the string vector and the map to find all anagrams. The complecity is only O(n+m), n is ths string number and m is the map entry number.

    Code:

    O(n^2) solution, Time Limit Execeed under larger test case

     1 class Solution {
     2 public:
     3     vector<string> anagrams(vector<string> &strs) {
     4         // Start typing your C/C++ solution below
     5         // DO NOT write int main() function
     6         int tag[strs.size()];
     7         vector<string> mid;
     8         vector<string> res;
     9         
    10         res.clear();
    11         for (int i=0; i<strs.size(); i++) {
    12             tag[i] = 0;
    13             mid.push_back(strs[i]);
    14             sort(mid[i].begin(), mid[i].end());
    15         }
    16             
    17         for (int i=0; i<strs.size(); i++) {
    18             bool find = false;
    19             if (tag[i] == 0) {
    20                 for (int j=i+1; j<strs.size(); j++) {
    21                     if (tag[j] == 0 && mid[i] == mid[j]) {
    22                             res.push_back(strs[j]);
    23                             find = true;
    24                             tag[j] = 1;
    25                     }
    26                 }
    27                 
    28             }
    29             
    30             if (find) {
    31                 tag[i] = 1;
    32                 res.push_back(strs[i]);
    33             }
    34         }
    35         
    36         return res;
    37     }
    38 };
    View Code

    O(n) solution

     1 class Solution {
     2 public:
     3     vector<string> anagrams(vector<string> &strs) {
     4         // Start typing your C/C++ solution below
     5         // DO NOT write int main() function
     6         vector<string> res;
     7         map<string, vector<string> > sm; 
     8         
     9         for (int i=0; i<strs.size(); i++) {
    10             string s = strs[i];
    11             sort(s.begin(), s.end());
    12             sm[s].push_back(strs[i]);
    13         }
    14         
    15         for (map<string, vector<string> >::iterator it=sm.begin(); 
    16                     it!=sm.end(); it++) {
    17             if ((*it).second.size() >= 2) {
    18                 for (int i=0; i<(*it).second.size(); i++) {
    19                     res.push_back((*it).second[i]);
    20                 }
    21             }
    22         }
    23         
    24         return res;
    25     }
    26 };
    View Code
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  • 原文地址:https://www.cnblogs.com/freeneng/p/3099602.html
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