hash table apply

Author: jackzhenguo

HashTable/HashTable.Lib/FindAllAnagramsSln.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace HashTable.Lib
+{
+    //    Given a string s and a non-empty string p, find all the start indices of p's anagrams in s.
+
+    //Strings consists of lowercase English letters only and the length of both strings s and p will not be larger than 20,100.
+
+    //The order of output does not matter.
+
+    //Example 1:
+
+    //Input:
+    //s: "cbaebabacd" p: "abc"
+
+    //Output:
+    //[0, 6]
+
+    //Explanation:
+    //The substring with start index = 0 is "cba", which is an anagram of "abc".
+    //The substring with start index = 6 is "bac", which is an anagram of "abc".
+    //Example 2:
+
+    //Input:
+    //s: "abab" p: "ab"
+
+    //Output:
+    //[0, 1, 2]
+
+    //Explanation:
+    //The substring with start index = 0 is "ab", which is an anagram of "ab".
+    //The substring with start index = 1 is "ba", which is an anagram of "ab".
+    //The substring with start index = 2 is "ab", which is an anagram of "ab".
+    public class FindAllAnagramsSln
+    {
+        //s = "cbaebabacd", p = "abc"
+        public IList<int> FindAnagrams(string s, string p){
+            IList<int> rtn = new List<int>();
+            int[] hash = new int[123]; //a~z: 97~122
+            foreach (var c in p){
+                hash[Convert.ToInt32(c)]++; //hash: key:char, value: occuring times
+            }
+            int eachBeg = 0, eachEnd = 0, count = p.Length;
+            while (eachEnd < s.Length){
+                char tmpchar = s[eachEnd];
+                if (hash[tmpchar] >= 1) 
+                    count--;
+                hash[tmpchar]--;
+                eachEnd++; //every time the eachEnd pointer to move toward right
+                if (count == 0) 
+                    rtn.Add(eachBeg);
+                //reset the hash. 
+
+                if (eachEnd - eachBeg == p.Length){ 
+                    char tmp = s[eachBeg];
+                    if (hash[tmp] >= 0)
+                        count++;
+                    hash[tmp]++;
+                    eachBeg++;
+                }
+            }
+            return rtn;
+        }
+    }
+}

HashTable/HashTable.Lib/PrimesCountSln.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace HashTable.Lib
+{
+    public class PrimesCountSln
+    {
+        public int CountPrimes(int n)
+        {
+            int rtncnt = 0;
+            bool[] notPrimes = new bool[n];
+            for (int i = 2; i < n; i++)
+            {
+                if (notPrimes[i]) continue;
+                rtncnt++;
+                for (int j = 2; i * j < n; j++)
+                {
+                    notPrimes[i * j] = true;
+                }
+            }
+            return rtncnt;
+        }
+    }
+}

HashTable/HashTable.Lib/ValidAnagramSln.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace HashTable.Lib
+{
+    public class ValidAnagramSln
+    {
+        public bool IsAnagram(string s, string t)
+        {
+            int[] hash = new int[123]; //a~z
+            if (s.Length != t.Length) return false;
+            foreach (var ch in s)
+            {
+                hash[Convert.ToInt32(ch)]++;
+            }
+            foreach (var ch in t)
+            {
+                if (hash[Convert.ToInt32(ch)]-- <= 0)
+                    return false;
+            }
+            return true;
+        }
+    }
+}