feat(C++): Add 1293

Mad amount of edge cases that I failed to consider...

C++/1293-ShortestPathInAGridWithObstaclesElimination/Solution.cpp

@@ -0,0 +1,76 @@
+#include <array>
+#include <cstddef>
+#include <queue>
+#include <tuple>
+#include <utility>
+#include <vector>
+
+using namespace std;
+class Solution {
+ private:
+  // Need to consider all 4 directions instead of just right and bottom. This
+  // is to deal with the situation where the obstacle blocks right/bottom, and
+  // the only path is left/top
+  static constexpr std::array<std::pair<int, int>, 4> directions{
+      {{0, 1}, {1, 0}, {0, -1}, {-1, 0}}};
+
+ public:
+  int shortestPath(vector<vector<int>>& grid, int k) {
+    // grid[i][j] = 0 (empty) | 1 (obstacle)
+    // Move in cardinal directions to an empty cell.
+    // k is the number of obstacles that can be eliminated.
+    //
+    // Start (0, 0), Goal (m-1, n-1)
+    // Intuition is just BFS with an extra state to represent the number of
+    // obstacles break remaining.
+    const size_t rows = grid.size();
+    const size_t cols = grid[0].size();
+    if (k >= rows + cols - 2) {
+      // manhattan dist between (0, 0) and (rows-1, cols-1)
+      // This optimization is necessary to avoid unnecessary traversal if we
+      // can determine that we can just break through all obstacles.
+      return rows + cols - 2;
+    }
+
+    std::queue<std::tuple<int, int, int>> frontier;
+    std::vector<std::vector<std::vector<bool>>> seen(
+        rows,
+        std::vector<std::vector<bool>>(cols, std::vector<bool>(k + 1, false)));
+    frontier.emplace(0, 0, k);
+    seen[0][0][k] = true;
+
+    int steps = 0;
+    while (!frontier.empty()) {
+      int size = frontier.size();
+      while (size--) {
+        const auto [r, c, breaks] = frontier.front();
+        frontier.pop();
+
+        if (r == rows - 1 && c == cols - 1) {
+          return steps;
+        }
+
+        for (const auto& [dr, dc] : directions) {
+          const int nr = r + dr;
+          const int nc = c + dc;
+
+          if (nr < 0 || nc < 0 || nr >= rows || nc >= cols) {
+            continue;
+          }
+
+          int newBreaks = breaks - grid[nr][nc];
+          if ((grid[nr][nc] == 1 && breaks <= 0) || seen[nr][nc][newBreaks]) {
+            // note we check newBreaks AFTER checkin of breaks <= 0.
+            // Avoid negative indexing.
+            continue;
+          }
+
+          frontier.emplace(nr, nc, newBreaks);
+          seen[nr][nc][newBreaks] = true;
+        }
+      }
+      ++steps;
+    }
+    return -1;
+  }
+};

README.md

@@ -341,6 +341,7 @@ Now solving in C++. Like it.
 | 1255 | MaximumScoreWordsFormedByLetters                                 |                                           [![C++](assets/c++.svg)](C++/1255-MaximumScoreWordsFormedByLetters/Solution.cpp)                                            |
 | 1257 | SmallestCommonRegion                                             |                                                 [![C++](assets/c++.svg)](C++/1257-SmallestCommonRegion/Solution.cpp)                                                  |
 | 1277 | CountSquareSubmatricesWithOnes                                   |                                            [![C++](assets/c++.svg)](C++/1277-CountSquareSubmatricesWithOnes/Solution.cpp)                                             |
+| 1293 | ShortestPathInAGridWithObstaclesElimination                      |                                      [![C++](assets/c++.svg)](C++/1293-ShortestPathInAGridWithObstaclesElimination/Solution.cpp)                                      |
 | 1310 | XORQueriesOfASubarray                                            |                                                 [![C++](assets/c++.svg)](C++/1310-XORQueriesOfASubarray/Solution.cpp)                                                 |
 | 1317 | ConvertIntegerToTheSumOfTwoNoZeroIntegers                        |                                       [![C++](assets/c++.svg)](C++/1317-ConvertIntegerToTheSumOfTwoNoZeroIntegers/Solution.cpp)                                       |
 | 1323 | Maximum69Number                                                  |                                                    [![C++](assets/c++.svg)](C++/1323-Maximum69Number/Solution.cpp)                                                    |