Adding 3rd assignment, stacks and queues

Stacks&Queues/FUtils.h

@@ -0,0 +1,183 @@
+#ifndef STACKS_QUEUES_FUTILS_H
+#define STACKS_QUEUES_FUTILS_H
+
+#include <iostream>
+#include <stdexcept>
+#include <string>
+#include "TQueue.h"
+#include "TStack.h"
+
+constexpr int GRID_ROWS = 100;
+constexpr int GRID_COLS = 100;
+
+
+// Stack is perfect here because of the structure and behaviour of stacks - LIFO
+// When we push the string in it will send the first char to the bottom of the stack
+// When we push the string back out it will pop the last char first, then the second to last, then third and so on
+// Time and space complexity is O(n) - each char pushed and popped exactly once and
+// helper string "reverse clone" is needed for output
+inline std::string ReverseString(const std::string& input)
+{
+    if (input.size() > MAX_SIZE)
+        throw std::overflow_error("Input longer than MAX_SIZE");
+    TStack s;
+    for (char c : input)
+        s.Push(c);
+    std::string output;
+    output.reserve(input.size());
+    while (!s.IsEmpty())
+    {
+        output.push_back(s.Pop());
+    }
+    return output;
+}
+
+// Time = O(n) - push 2 .. n once and pop each once
+// Space = O(1) - fixed size array inside TStack
+inline long long Factorial(const int base)
+{
+    if (base < 0)
+        throw std::invalid_argument("n must be >= 0");
+    if (base == 0 || base == 1)
+        return 1;
+    if (base > MAX_SIZE)
+        throw std::overflow_error("n exceeds MAX_SIZE");
+    TStack s;
+    for (int i = 2; i <= base; ++i)
+        s.Push(i);
+    long long result = 1;
+    while (!s.IsEmpty())
+        result *= s.Pop();
+    return result;
+}
+
+// Time = O(arrivals + toServe)
+// Space = O(1) - fixed size queue
+inline void SimulateWaitLine(const int arrivals, int toServe, TQueue& queue)
+{
+    static int nextId = 1;
+    // arrivals
+    for (int i = 1; i <= arrivals; ++i) {
+        queue.Enqueue(nextId);
+        std::cout << "Arrives: " << nextId << std::endl;
+        nextId++;
+    }
+
+    // served
+    for (int i = 0; i < toServe && !queue.IsEmpty(); ++i) {
+        std::cout << "Served: " << queue.Dequeue() << std::endl;
+    }
+}
+
+// O(1) both - just checking if true or false
+inline bool InBounds (int r, int c)
+{
+    return r >= 0 && r < GRID_ROWS && c >= 0 && c < GRID_COLS;
+}
+
+// O(r * c)
+inline void ResetVisited(bool visited[GRID_ROWS][GRID_COLS])
+{
+    for (int r = 0; r < GRID_ROWS; ++r) {
+        for (int c = 0; c < GRID_COLS; ++c) {
+            visited[r][c] = false;
+        }
+    }
+}
+
+inline int EncodePos(int r, int c) {
+    return r * GRID_COLS + c;
+}
+
+inline void DecodePos(int code, int& r, int& c) {
+    r = code / GRID_COLS;
+    c = code % GRID_COLS;
+}
+
+// Time = O( r * c) worst case
+// Space is O(1)
+inline bool DFSFindZero(const int grid[GRID_ROWS][GRID_COLS], bool visited[GRID_ROWS][GRID_COLS],
+                        int startR, int startC, int& outR, int& outC)
+{
+    TStack s;
+
+    // mark start immediately to avoid multiple pushes
+    visited[startR][startC] = true;
+    s.Push(EncodePos(startR, startC));
+
+    while (!s.IsEmpty())
+    {
+        int code = s.Pop();
+        int r, c; DecodePos(code, r, c);
+
+        if (grid[r][c] == 0) {
+            outR = r; outC = c;
+            return true;
+        }
+
+        // Push neighbours, marking visited when discovered
+        if (InBounds(r - 1, c) && !visited[r - 1][c]) {
+            visited[r - 1][c] = true;
+            s.Push(EncodePos(r - 1, c)); // up
+        }
+        if (InBounds(r, c + 1) && !visited[r][c + 1]) {
+            visited[r][c + 1] = true;
+            s.Push(EncodePos(r, c + 1)); // right
+        }
+        if (InBounds(r + 1, c) && !visited[r + 1][c]) {
+            visited[r + 1][c] = true;
+            s.Push(EncodePos(r + 1, c)); // down
+        }
+        if (InBounds(r, c - 1) && !visited[r][c - 1]) {
+            visited[r][c - 1] = true;
+            s.Push(EncodePos(r, c - 1)); // left
+        }
+    }
+    return false;
+}
+
+// Same complexity as DFS
+inline bool BFSFindZero(const int grid[GRID_ROWS][GRID_COLS], bool visited[GRID_ROWS][GRID_COLS],
+                        int startR, int startC, int& outR, int& outC)
+{
+    TQueue q;
+
+    // mark start immediately to avoid duplicate enqueues
+    visited[startR][startC] = true;
+    q.Enqueue(EncodePos(startR, startC));
+
+    while (!q.IsEmpty())
+    {
+        int code = q.Dequeue();
+        int r, c; DecodePos(code, r, c);
+
+        if (grid[r][c] == 0) {
+            outR = r; outC = c;
+            return true;
+        }
+
+        // Enqueue neighbours, marking visited on discovery
+        if (InBounds(r - 1, c) && !visited[r - 1][c]) {
+            visited[r - 1][c] = true;
+            q.Enqueue(EncodePos(r - 1, c)); // up
+        }
+        if (InBounds(r, c + 1) && !visited[r][c + 1]) {
+            visited[r][c + 1] = true;
+            q.Enqueue(EncodePos(r, c + 1)); // right
+        }
+        if (InBounds(r + 1, c) && !visited[r + 1][c]) {
+            visited[r + 1][c] = true;
+            q.Enqueue(EncodePos(r + 1, c)); // down
+        }
+        if (InBounds(r, c - 1) && !visited[r][c - 1]) {
+            visited[r][c - 1] = true;
+            q.Enqueue(EncodePos(r, c - 1)); // left
+        }
+    }
+    return false;
+}
+
+
+
+
+#endif //STACKS_QUEUES_FUTILS_H