Find Common Characters - Array - Easy - LeetCode

Given an array A of strings made only from lowercase letters, return a list of all characters that show up in all strings within the list (including duplicates). For example, if a character occurs 3 times in all strings but not 4 times, you need to include that character three times in the final answer.

You may return the answer in any order.

Example 1:

Input: ["bella","label","roller"]

Output: ["e","l","l"]

Example 2:

Input: ["cool","lock","cook"]

Output: ["c","o"]

Note:

1 <= A.length <= 100

1 <= A[i].length <= 100

A[i][j] is a lowercase letter

Solution:

using System;
using System.Collections.Generic;
using System.Text;

namespace LeetCode.AskGif.Easy.Array
{
 public class CommonCharsSoln
 {
 public IList<string> CommonChars(string[] A)
 {
 var mapList = new List<Dictionary<char, int>>();
 for (int i = 0; i < A.Length; i++)
 {
 var map = new Dictionary<char, int>();
 for (int j = 0; j < A[i].Length; j++)
 {
 if (map.ContainsKey(A[i][j]))
 {
 map[A[i][j]]++;
 }
 else
 {
 map.Add(A[i][j], 1);
 }
 }

 mapList.Add(map);
 }

 var res = new List<string>();

 for (char i = 'a'; i <= 'z'; i++)
 {
 int min = int.MaxValue;
 for (int j = 0; j < mapList.Count; j++)
 {
 if (mapList[j].ContainsKey(i))
 {
 if (mapList[j][i] < min)
 {
 min = mapList[j][i];
 }
 }
 else
 {
 min = 0;
 }
 }

 if(min == int.MaxValue)
 {
 min = 0;
 }

 for (int x = 0; x < min; x++)
 {
 res.Add(i.ToString());
 }

 }

 return res;
 }
 }
}

Time Complexity: O(m*n) Where m is the number of string and n is the size of the string.

Space Complexity: O(m*n)

Unit Tests:

using LeetCode.AskGif.Easy.Array;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using System;
using System.Collections.Generic;
using System.Text;

namespace CodingUnitTest.Easy.Array
{
 [TestClass]
 public class CommonCharsSolnTests
 {
 [TestMethod]
 public void CommonCharsSoln_First()
 {
 var arr = new string[] { "bella", "label", "roller" };
 var expected = new Dictionary<string, int>();
 expected.Add("e",1);
 expected.Add("l", 2);

 var res = new CommonCharsSoln().CommonChars(arr);
 AreEqual(expected, res);
 }

 [TestMethod]
 public void CommonCharsSoln_Second()
 {
 var arr = new string[] { "cool", "lock", "cook" };
 var expected = new Dictionary<string, int>();
 expected.Add("c", 1);
 expected.Add("o", 1);

 var res = new CommonCharsSoln().CommonChars(arr);
 AreEqual(expected, res);
 }

 private void AreEqual(Dictionary<string, int> expected, IList<string> res)
 {
 var map = new Dictionary<string, int>();
 for (int i = 0; i < res.Count; i++)
 {
 if (map.ContainsKey(res[i]))
 {
 map[res[i]]++;
 }
 else
 {
 map.Add(res[i], 1);
 }
 }

 foreach (var item in map)
 {
 Assert.IsTrue(expected.ContainsKey(item.Key));
 Assert.AreEqual(expected[item.Key], item.Value);
 }

 foreach (var item in expected)
 {
 Assert.IsTrue(map.ContainsKey(item.Key));
 Assert.AreEqual(map[item.Key], item.Value);
 }
 } 
 }
}