problems(cpp): add “59. Spiral Matrix II”

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/spiral-matrix-ii.cpp

@@ -0,0 +1,102 @@
+#include <cassert>
+#include <iostream>
+#include <vector>
+
+class Solution {
+  struct indices {
+    int x;
+    int y;
+
+    bool operator==(const indices& other) const = default;
+    indices& operator+=(const indices& other) {
+      x += other.x;
+      y += other.y;
+      return *this;
+    }
+
+    friend indices operator+(indices left, const indices& right) {
+      return left += right;
+    }
+
+    int& operator[](std::vector<std::vector<int>>& mat) const {
+      return mat[y][x];
+    }
+  };
+
+  struct spiral_indices {
+    spiral_indices(const std::vector<std::vector<int>>& matrix)
+        : x_bounds{-1, static_cast<int>(matrix.size() ? matrix[0].size() : 0)},
+          y_bounds{-1, static_cast<int>(matrix.size())} {}
+
+    bool done() const { return !in_bounds(idx); }
+
+    spiral_indices& operator++() {
+      // update bounds and change the direction if cannot move
+      if (!in_bounds(idx + d)) {
+        // change the direction
+        d = {-d.y, d.x};
+
+        // get the magnitude of the vector
+        auto flat_d = d.x + d.y;
+
+        // decide whether we're moving x or y bounds
+        auto& bounds = d.x ? x_bounds : y_bounds;
+        if (flat_d > 0) {
+          bounds.x++;
+        } else {
+          bounds.y--;
+        }
+      }
+
+      idx += d;
+
+      return *this;
+    }
+
+    int& operator[](std::vector<std::vector<int>>& mat) const {
+      return idx[mat];
+    }
+
+   private:
+    indices idx{0, 0};
+    indices d{1, 0};
+    indices x_bounds, y_bounds;
+
+    bool in_bounds(const indices& idx) const {
+      return (x_bounds.x < idx.x && idx.x < x_bounds.y) &&
+             (y_bounds.x < idx.y && idx.y < y_bounds.y);
+    }
+  };
+
+ public:
+  std::vector<std::vector<int>> generateMatrix(int n) {
+    auto length = static_cast<std::size_t>(n);
+    std::vector<std::vector<int>> spiral{length, std::vector<int>(length, 0)};
+
+    int i = 1;
+    for (spiral_indices idx{spiral}; !idx.done(); ++idx) {
+      idx[spiral] = i++;
+    }
+
+    return spiral;
+  }
+};
+
+int main() {
+  Solution s;
+
+  assert((s.generateMatrix(0) == std::vector<std::vector<int>>{}));
+  assert((s.generateMatrix(1) == std::vector<std::vector<int>>{{1}}));
+  assert(
+      (s.generateMatrix(2) == std::vector<std::vector<int>>{{1, 2}, {4, 3}}));
+
+  for (auto&& row : s.generateMatrix(3)) {
+    for (auto x : row) std::cout << x << " ";
+    std::cout << "\n";
+  }
+
+  assert((s.generateMatrix(3) ==
+          std::vector<std::vector<int>>{{1, 2, 3}, {8, 9, 4}, {7, 6, 5}}));
+
+  return 0;
+}