A solution added for LC #3905

Author: rayworks

src/main/java/org/sean/graph/MultiSrcFloodFill.java

@@ -0,0 +1,77 @@
+package org.sean.graph;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+import java.util.HashMap;
+import java.util.Map;
+
+/***
+ * 3905. Multi Source Flood Fill
+ */
+public class MultiSrcFloodFill {
+
+    public int[][] colorGrid(int n, int m, int[][] sources) {
+        int[][] grid = new int[n][m];
+
+        Deque<int[]> deque = new ArrayDeque<>();
+
+        for (int[] src : sources) {
+            int r = src[0];
+            int c = src[1];
+            grid[r][c] = src[2];
+
+            // add all sources
+            deque.add(new int[]{r, c});
+        }
+
+        int[][] offsets = new int[][]{
+                {-1, 0}, {0, 1}, {1, 0}, {0, -1}
+        };
+
+        int step = 0;
+        // <loc, step>
+        Map<Integer, Integer> cache = new HashMap<>();
+
+        // BFS
+        while (!deque.isEmpty()) {
+            int sz = deque.size();
+
+            step++;
+            for (int i = 0; i < sz; i++) {
+                int[] grp = deque.poll();
+
+                if (grp == null) continue;
+                int currRow = grp[0];
+                int currCol = grp[1];
+                int currVal = grid[currRow][currCol];
+
+                for (int[] off : offsets) {
+                    int nRow = currRow + off[0];
+                    int nCol = currCol + off[1];
+                    if (nRow >= n || nRow < 0 || nCol >= m || nCol < 0)
+                        continue;
+
+                    // at the same time step
+                    int nextStep = step + 1;
+                    int key = nRow * m + nCol;
+
+                    if (grid[nRow][nCol] == 0) {
+                        grid[nRow][nCol] = currVal;
+                        cache.put(key, nextStep);
+
+                        // added once for next round coloring
+                        deque.add(new int[]{nRow, nCol});
+                    } else {
+                        if (cache.getOrDefault(key, 0) == nextStep
+                                && grid[nRow][nCol] < currVal) {
+                            grid[nRow][nCol] = currVal;
+                        }
+                    }
+                }
+
+            }
+        }
+
+        return grid;
+    }
+}

src/test/java/org/sean/graph/MultiSrcFloodFillTest.java

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+package org.sean.graph;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+import static org.junit.Assert.assertArrayEquals;
+
+public class MultiSrcFloodFillTest {
+
+    private MultiSrcFloodFill floodFill;
+
+    @Before
+    public void setUp() throws Exception {
+        floodFill = new MultiSrcFloodFill();
+    }
+
+    @Test
+    public void colorGrid() {
+        int[][] res = floodFill.colorGrid(3, 3, new int[][]{
+                {0, 1, 3}, {1, 1, 5}
+        });
+
+        assertArrayEquals(new int[][]{
+                {3, 3, 3}, {5, 5, 5}, {5, 5, 5}
+        }, res);
+    }
+}