Add DFS and Quick Sort implementations with recursive and iterative m…

Algorithms/DFS.cpp

@@ -0,0 +1,65 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+void dfs_recursive(int u, const vector<vector<int>>& adj, vector<bool>& vis, vector<int>& order) {
+    vis[u] = true;
+    order.push_back(u);
+    for (int v : adj[u]) if (!vis[v]) dfs_recursive(v, adj, vis, order);
+}
+
+vector<int> dfs_iterative(int start, const vector<vector<int>>& adj) {
+    int n = adj.size();
+    vector<bool> vis(n, false);
+    vector<int> order;
+    stack<int> st;
+    st.push(start);
+    while (!st.empty()) {
+        int u = st.top(); st.pop();
+        if (vis[u]) continue;
+        vis[u] = true;
+        order.push_back(u);
+        // push neighbors in reverse to mimic recursive order
+        for (auto it = adj[u].rbegin(); it != adj[u].rend(); ++it) if (!vis[*it]) st.push(*it);
+    }
+    return order;
+}
+
+int main() {
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    int n, m;
+    cout << "DFS (recursive + iterative)\nEnter number of nodes: ";
+    if (!(cin >> n) || n <= 0) return 0;
+    cout << "Enter number of edges: ";
+    cin >> m;
+
+    vector<vector<int>> adj(n);
+    cout << "Enter edges (u v) 0-based indices, one per line:\n";
+    for (int i = 0; i < m; ++i) {
+        int u, v; cin >> u >> v;
+        if (u < 0 || u >= n || v < 0 || v >= n) continue;
+        adj[u].push_back(v);
+        adj[v].push_back(u); // treat as undirected by default
+    }
+
+    int start;
+    cout << "Enter start node: ";
+    cin >> start;
+    if (start < 0 || start >= n) start = 0;
+
+    vector<bool> vis(n, false);
+    vector<int> order_rec;
+    dfs_recursive(start, adj, vis, order_rec);
+
+    cout << "Recursive DFS order: ";
+    for (int x : order_rec) cout << x << ' ';
+    cout << '\n';
+
+    vector<int> order_it = dfs_iterative(start, adj);
+    cout << "Iterative DFS order: ";
+    for (int x : order_it) cout << x << ' ';
+    cout << '\n';
+
+    return 0;
+}

Algorithms/Quick_Sort.cpp

@@ -0,0 +1,53 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+int partition(vector<int>& a, int low, int high) {
+    int pivot = a[high]; // choose last element as pivot
+    int i = low - 1;
+    for (int j = low; j < high; ++j) {
+        if (a[j] <= pivot) {
+            ++i;
+            swap(a[i], a[j]);
+        }
+    }
+    swap(a[i + 1], a[high]);
+    return i + 1;
+}
+
+void quickSort(vector<int>& a, int low, int high) {
+    if (low < high) {
+        int pi = partition(a, low, high);
+        quickSort(a, low, pi - 1);
+        quickSort(a, pi + 1, high);
+    }
+}
+
+void printArray(const vector<int>& a) {
+    for (int v : a) cout << v << " ";
+    cout << '\n';
+}
+
+int main() {
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    int n;
+    cout << "Quick Sort - Enter number of elements: ";
+    if (!(cin >> n) || n <= 0) {
+        cout << "Invalid size\n";
+        return 0;
+    }
+
+    vector<int> a(n);
+    cout << "Enter " << n << " integers:\n";
+    for (int i = 0; i < n; ++i) cin >> a[i];
+
+    cout << "Original array: ";
+    printArray(a);
+
+    quickSort(a, 0, n - 1);
+
+    cout << "Sorted array: ";
+    printArray(a);
+    return 0;
+}