day 13

Author: sachuverma

Leetcode Daily Challenge/February-2021/13. Shortest Path in Binary Matrix.cpp

@@ -0,0 +1,92 @@
+/*
+Shortest Path in Binary Matrix
+==============================
+
+In an N by N square grid, each cell is either empty (0) or blocked (1).
+
+A clear path from top-left to bottom-right has length k if and only if it is composed of cells C_1, C_2, ..., C_k such that:
+
+Adjacent cells C_i and C_{i+1} are connected 8-directionally (ie., they are different and share an edge or corner)
+C_1 is at location (0, 0) (ie. has value grid[0][0])
+C_k is at location (N-1, N-1) (ie. has value grid[N-1][N-1])
+If C_i is located at (r, c), then grid[r][c] is empty (ie. grid[r][c] == 0).
+Return the length of the shortest such clear path from top-left to bottom-right.  If such a path does not exist, return -1.
+
+Example 1:
+Input: [[0,1],[1,0]]
+Output: 2
+
+Example 2:
+Input: [[0,0,0],[1,1,0],[1,1,0]]
+Output: 4
+
+Note:
+1 <= grid.length == grid[0].length <= 100
+grid[r][c] is 0 or 1
+
+Hint #1  
+Do a breadth first search to find the shortest path.
+
+*/
+
+class Solution
+{
+public:
+  int shortestPathBinaryMatrix(vector<vector<int>> &grid)
+  {
+    if (grid[0][0] == 1)
+      return -1;
+
+    int n = grid.size();
+    queue<vector<int>> pending;
+    pending.push({0, 0});
+    grid[0][0] = 1;
+
+    int ans = INT_MAX;
+    int steps = 0;
+
+    int dir[] = {-1, 0, 1};
+
+    while (pending.size())
+    {
+      auto size = pending.size();
+
+      for (int i = 0; i < size; ++i)
+      {
+        auto curr = pending.front();
+        pending.pop();
+        int x = curr[0], y = curr[1];
+
+        if (x == n - 1 && y == n - 1)
+        {
+          steps++;
+          ans = min(ans, steps);
+          continue;
+        }
+
+        for (int j = 0; j < 3; ++j)
+        {
+          for (int l = 0; l < 3; ++l)
+          {
+
+            int nextX = x + dir[j];
+            int nextY = y + dir[l];
+
+            if (nextX < 0 || nextY < 0 || nextX >= n || nextY >= n || (nextX == x && nextY == y) || grid[nextX][nextY])
+            {
+              continue;
+            }
+            else
+            {
+              grid[nextX][nextY] = 1;
+              pending.push({nextX, nextY});
+            }
+          }
+        }
+      }
+      steps++;
+    }
+
+    return ans != INT_MAX ? ans : -1;
+  }
+};

Leetcode Daily Challenge/February-2021/README.MD

@@ -14,5 +14,6 @@
 | 10.  | [Copy List with Random Pointer](https://leetcode.com/explore/challenge/card/february-leetcoding-challenge-2021/585/week-2-february-8th-february-14th/3635/) | [cpp](./10.%20Copy%20List%20with%20Random%20Pointer.cpp) | 
 | 11.  | [Valid Anagram](https://leetcode.com/explore/challenge/card/february-leetcoding-challenge-2021/585/week-2-february-8th-february-14th/3636/) | [cpp](./11.%20Valid%20Anagram.cpp) | 
 | 12.  | [Number of Steps to Reduce a Number to Zero](https://leetcode.com/explore/challenge/card/february-leetcoding-challenge-2021/585/week-2-february-8th-february-14th/3637/) | [cpp](./12.%20Number%20of%20Steps%20to%20Reduce%20a%20Number%20to%20Zero.cpp) | 
+| 13.  | [Shortest Path in Binary Matrix](https://leetcode.com/explore/challenge/card/february-leetcoding-challenge-2021/585/week-2-february-8th-february-14th/3638/) | [cpp](./13.%20Shortest%20Path%20in%20Binary%20Matrix.cpp) |