Add Geohashing (#486)

Author: ngtduc693

Algorithms.Tests/Other/GeohashTests.cs

@@ -0,0 +1,59 @@
+using Algorithms.Other;
+using NUnit.Framework;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Algorithms.Tests.Other
+{
+    [TestFixture]
+    public class GeohashTests
+    {
+        [Test]
+        public void Encode_ShouldReturnCorrectGeohash_ForHoChiMinhCity()
+        {
+            double latitude = 10.8231;
+            double longitude = 106.6297;
+            string result = Geohash.Encode(latitude, longitude);
+            Assert.That(result, Is.EqualTo("w3gvd6m3hh54"));
+        }
+
+        [Test]
+        public void Encode_ShouldReturnCorrectGeohash_ForHanoi()
+        {
+            double latitude = 21.0285;
+            double longitude = 105.8542;
+            string result = Geohash.Encode(latitude, longitude);
+            Assert.That(result, Is.EqualTo("w7er8u0evss2"));
+        }
+
+        [Test]
+        public void Encode_ShouldReturnCorrectGeohash_ForDaNang()
+        {
+            double latitude = 16.0544;
+            double longitude = 108.2022;
+            string result = Geohash.Encode(latitude, longitude);
+            Assert.That(result, Is.EqualTo("w6ugq4w7wj04"));
+        }
+
+        [Test]
+        public void Encode_ShouldReturnCorrectGeohash_ForNhaTrang()
+        {
+            double latitude = 12.2388;
+            double longitude = 109.1967;
+            string result = Geohash.Encode(latitude, longitude);
+            Assert.That(result, Is.EqualTo("w6jtsu485t8v"));
+        }
+
+        [Test]
+        public void Encode_ShouldReturnCorrectGeohash_ForVungTau()
+        {
+            double latitude = 10.3460;
+            double longitude = 107.0843;
+            string result = Geohash.Encode(latitude, longitude);
+            Assert.That(result, Is.EqualTo("w3u4ug2mv41m"));
+        }
+    }
+}

Algorithms/Other/Geohash.cs

@@ -0,0 +1,84 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Algorithms.Other
+{
+    public static class Geohash
+    {
+        private const string Base32Characters = "0123456789bcdefghjkmnpqrstuvwxyz"; // Convert latitude and longitude coordinates into a concise string
+        private const int GeohashLength = 12; // ± 1.86 cm
+
+        /// <summary>
+        /// Encodes the provided latitude and longitude coordinates into a Geohash string.
+        /// Geohashing is a method to encode geographic coordinates (latitude, longitude).
+        /// into a short string of letters and digits. Each character in the resulting Geohash .
+        /// string adds more precision to the location. The longer the Geohash, the smaller the area.
+        /// </summary>
+        /// <param name="latitude">The latitude of the location to encode. It must be a value between -90 and 90.</param>
+        /// <param name="longitude">The longitude of the location to encode. It must be a value between -180 and 180.</param>
+        /// <returns>
+        /// A Geohash string of length 12 representing the location with high precision.
+        /// A longer Geohash provides higher precision in terms of geographic area.
+        /// and a 12-character Geohash can be accurate down to around 1.86 cm.
+        /// </returns>
+        public static string Encode(double latitude, double longitude)
+        {
+            double[] latitudeRange = new[] { -90.0, 90.0 };
+            double[] longitudeRange = new[] { -180.0, 180.0 };
+            bool isEncodingLongitude = true;
+            int currentBit = 0;
+            int base32Index = 0;
+            StringBuilder geohashResult = new StringBuilder();
+
+            while (geohashResult.Length < GeohashLength)
+            {
+                double midpoint;
+
+                if (isEncodingLongitude)
+                {
+                    midpoint = (longitudeRange[0] + longitudeRange[1]) / 2;
+                    if (longitude > midpoint)
+                    {
+                        base32Index |= 1 << (4 - currentBit);
+                        longitudeRange[0] = midpoint;
+                    }
+                    else
+                    {
+                        longitudeRange[1] = midpoint;
+                    }
+                }
+                else
+                {
+                    midpoint = (latitudeRange[0] + latitudeRange[1]) / 2;
+                    if (latitude > midpoint)
+                    {
+                        base32Index |= 1 << (4 - currentBit);
+                        latitudeRange[0] = midpoint;
+                    }
+                    else
+                    {
+                        latitudeRange[1] = midpoint;
+                    }
+                }
+
+                isEncodingLongitude = !isEncodingLongitude;
+
+                if (currentBit < 4)
+                {
+                    currentBit++;
+                }
+                else
+                {
+                    geohashResult.Append(Base32Characters[base32Index]);
+                    currentBit = 0;
+                    base32Index = 0;
+                }
+            }
+
+            return geohashResult.ToString();
+        }
+    }
+}

README.md

@@ -222,6 +222,7 @@ find more than one implementation for the same objective but using different alg
     * [Welford's Variance](./Algorithms/Other/WelfordsVariance.cs)
     * [Julian Easter](./Algorithms/Other/JulianEaster.cs)
     * [Pollard's Rho](./Algorithms/Other/PollardsRhoFactorizing.cs)
+    * [GeoLocation Hash](./Algorithms/Other/Geohash.cs)
   * [Problems](./Algorithms/Problems)
     * [Stable Marriage](./Algorithms/Problems/StableMarriage)
       * [Gale-Shapley](./Algorithms/Problems/StableMarriage/GaleShapley.cs)