Merge pull request #235 from harshendram/Algo/KNN

Added the implementation of KNN advance algorithm

Author: Pradeepsingh61

CPP/algorithms/searching/KNNalgorithm.cpp

@@ -0,0 +1,78 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+// A simple structure for data points
+struct Point
+{
+    vector<double> features; // coordinates/features
+    int label;               // class label (e.g., 0 or 1)
+};
+
+// Function to compute Euclidean distance
+double euclideanDistance(const vector<double> &a, const vector<double> &b)
+{
+    double sum = 0.0;
+    for (size_t i = 0; i < a.size(); i++)
+    {
+        sum += (a[i] - b[i]) * (a[i] - b[i]);
+    }
+    return sqrt(sum);
+}
+
+// k-NN classification
+int classifyKNN(const vector<Point> &dataset, const vector<double> &query, int k)
+{
+    // Compute distances from query to all dataset points
+    vector<pair<double, int>> distances;
+    for (const auto &p : dataset)
+    {
+        double dist = euclideanDistance(p.features, query);
+        distances.push_back({dist, p.label});
+    }
+
+    // Sort by distance
+    sort(distances.begin(), distances.end());
+
+    // Count labels among k nearest neighbors
+    unordered_map<int, int> freq;
+    for (int i = 0; i < k; i++)
+    {
+        freq[distances[i].second]++;
+    }
+
+    // Find majority class
+    int maxCount = 0, predictedLabel = -1;
+    for (auto &entry : freq)
+    {
+        if (entry.second > maxCount)
+        {
+            maxCount = entry.second;
+            predictedLabel = entry.first;
+        }
+    }
+
+    return predictedLabel;
+}
+
+int main()
+{
+    // Example dataset: 2D points with labels (0 or 1)
+    vector<Point> dataset = {
+        {{1.0, 2.0}, 0},
+        {{2.0, 3.0}, 0},
+        {{3.0, 3.0}, 0},
+        {{6.0, 5.0}, 1},
+        {{7.0, 7.0}, 1},
+        {{8.0, 6.0}, 1}};
+
+    // Query point to classify
+    vector<double> query = {5.0, 5.0};
+
+    int k = 3; // Number of neighbors
+    int predictedLabel = classifyKNN(dataset, query, k);
+
+    cout << "Query Point: (" << query[0] << ", " << query[1] << ")" << endl;
+    cout << "Predicted Class: " << predictedLabel << endl;
+
+    return 0;
+}