Merge pull request chipbk10#110 from chipbk10/UnionFind

Solve Problem 1391 - Check if valid path in grid

Author: chipbk10

src/data/UnionFind.java

@@ -43,4 +43,7 @@ public boolean union(int i, int j) {
         return true;
     }
 
+    public boolean isConnected(int i, int j) {
+        return find(i) == find(j);
+    }
 }

src/graph/unionfind/Problem1391_CheckIfValidPathInGrid.java

@@ -0,0 +1,37 @@
+package graph.unionfind;
+
+import data.UnionFind;
+
+public class Problem1391_CheckIfValidPathInGrid {
+
+    // l 0 r(l) 1 r
+    // i = 2*i+1
+    // j = 2*j+1
+    public boolean hasValidPath(int[][] grid) {
+        int m = grid.length;
+        int n = grid[0].length;
+        int t = 2*n + 1;
+        UnionFind uf = new UnionFind((2*m + 1)*(2*n + 1));
+        for (int i = 0; i < m; i++) {
+            for (int j = 0; j < n; j++) {
+                if (grid[i][j] == 1 || grid[i][j] == 3 || grid[i][j] == 5) {
+                    uf.union(g(2*i + 1, 2*j + 1, t), g(2*i + 1, 2*j, t));
+                }
+                if (grid[i][j] == 1 || grid[i][j] == 4 || grid[i][j] == 6) {
+                    uf.union(g(2*i + 1, 2*j + 1, t), g(2*i + 1, 2*j + 2, t));
+                }
+                if (grid[i][j] == 2 || grid[i][j] == 3 || grid[i][j] == 4) {
+                    uf.union(g(2*i + 1, 2*j + 1, t), g(2*i + 2, 2*j + 1, t));
+                }
+                if (grid[i][j] == 2 || grid[i][j] == 5 || grid[i][j] == 6) {
+                    uf.union(g(2*i + 1, 2*j + 1, t), g(2*i, 2*j + 1, t));
+                }
+            }
+        }
+        return uf.isConnected(g(1, 1, t), g(2*m - 1, 2*n - 1, t));
+    }
+
+    public int g(int r, int c, int n) {
+        return r*n + c;
+    }
+}