标签：sep memory add sequence ict ase more dbr hash
Given a string s and a dictionary of words dict, determine if s can be segmented into a space-separated sequence of one or more dictionary words.
For example, given s = "leetcode", dict = ["leet", "code"].
Return true because "leetcode" can be segmented as "leet code".
Solution:
Need to use DP because derictly loop through the string may not return the correct answer.
Test case: s="aaaaaaa", dict = ["aaa", "aaaa"]
Two solutions:
First Dynamic programming:
dp[0] = true;// always true, because empty string can always add space to it.
dp[1] = dp[0]&&dict.Contains(s.Substring(0, 1);
dp[2] =( dp[1]&&dict.Contains(s.Substring(1,1))) ||(dp[0]&& dict.Contains(s.Substring(0,2)));
so need to loop through dp[j]&&wordDict.Contains(s.Substring(j,i-j)) untill dp[i] is true where j from 0 to i;
1 public class Solution { 2 public bool WordBreak(string s, ISet<string> wordDict) 3 { 4 ISet<int> set = new HashSet<int>(); 5 if(string.IsNullOrEmpty(s)) 6 { 7 return true; 8 } 9 int l = s.Length; 10 bool[] dp = new bool[l+1]; 11 dp[0] = true; 12 for(int i=1; i<l+1; i++) 13 { 14 for(int j=0; j<i; j++) 15 { 16 dp[i]=dp[j]&&wordDict.Contains(s.Substring(j,i-j)); 17 if(dp[i]) 18 { 19 break; 20 } 21 } 22 } 23 return dp[l]; 24 } 25 26 }
Second DFS:
Use recursion in Dfs to mark the indexes those already looped through and returned false;
1 public class Solution { 2 public bool WordBreak(string s, ISet<string> wordDict) 3 { 4 ISet<int> set = new HashSet<int>(); 5 return Dfs(s, 0, wordDict, set); 6 7 } 8 private bool Dfs(string s, int index, ISet<string> dict, ISet<int> set) 9 { 10 // base case 11 if (index == s.Length) return true; 12 // check memory 13 if (set.Contains(index)) return false; 14 // recursion 15 for (int i = index + 1; i <= s.Length; i++) 16 { 17 String t = s.Substring(index, i-index); 18 if (dict.Contains(t)) 19 if (Dfs(s, i, dict, set)) 20 return true; 21 else 22 set.Add(i); 23 } 24 set.Add(index); 25 return false; 26 } 27 }
标签：sep memory add sequence ict ase more dbr hash
原文地址：http://www.cnblogs.com/MiaBlog/p/6120498.html
