Given an array of integers arr, a lucky integer is an integer which has a frequency in the array equal to its value.
Return a lucky integer in the array. If there are multiple lucky integers return the largest of them. If there is no lucky integer return -1.
Example 1:
Input: arr = [2,2,3,4]
Output: 2
Explanation: The only lucky number in the array is 2 because frequency[2] == 2.
Example 2:
Input: arr = [1,2,2,3,3,3]
Output: 3
Explanation: 1, 2, and 3 are all lucky numbers, return the largest of them.
Example 3:
Input: arr = [2,2,2,3,3]
Output: -1
Explanation: There are no lucky numbers in the array.
Example 4:
Input: arr = [5]
Output: -1
Example 5:
Input: arr = [7,7,7,7,7,7,7]
Output: 7
Constraints:
1 <= arr.length <= 500
1 <= arr[i] <= 500
Solution:
using System;
using System.Collections.Generic;
using System.Text;
namespace LeetCode.AskGif.Easy.Array
{
public class FindLuckySoln
{
public int FindLucky(int[] arr)
{
var map = new Dictionary<int, int>();
for (int i = 0; i < arr.Length; i++)
{
if (map.ContainsKey(arr[i]))
{
map[arr[i]]++;
}
else
{
map.Add(arr[i], 1);
}
}
int max = -1;
foreach (var item in map)
{
if(item.Key == item.Value && item.Key > max)
{
max = item.Key;
}
}
return max;
}
}
}
Time Complexity: O(n)
Space Complexity: O(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 FindLuckySolnTests
{
[TestMethod]
public void FindLuckySoln_First()
{
var arr = new int[] { 2, 2, 3, 4 };
var output = 2;
var res = new FindLuckySoln().FindLucky(arr);
Assert.AreEqual(res, output);
}
[TestMethod]
public void FindLuckySoln_Second()
{
var arr = new int[] { 1, 2, 2, 3, 3, 3 };
var output = 3;
var res = new FindLuckySoln().FindLucky(arr);
Assert.AreEqual(res, output);
}
[TestMethod]
public void FindLuckySoln_Third()
{
var arr = new int[] { 2, 2, 2, 3, 3 };
var output = -1;
var res = new FindLuckySoln().FindLucky(arr);
Assert.AreEqual(res, output);
}
[TestMethod]
public void FindLuckySoln_Fourth()
{
var arr = new int[] { 5 };
var output = -1;
var res = new FindLuckySoln().FindLucky(arr);
Assert.AreEqual(res, output);
}
[TestMethod]
public void FindLuckySoln_Fifth()
{
var arr = new int[] { 7, 7, 7, 7, 7, 7, 7 };
var output = 7;
var res = new FindLuckySoln().FindLucky(arr);
Assert.AreEqual(res, output);
}
}
}
