Time: 106 ms (46.91%), Space: 44.7 MB (49.38%) - LeetHub

Author: Sangram03

2061-painting-a-grid-with-three-different-colors/2061-painting-a-grid-with-three-different-colors.java

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+class Solution {
+    public int colorTheGrid(int m, int n) {
+        final int mod = 1_000_000_007;
+        int total = 1;
+        for (int i = 0; i < m; i++) total *= 3;
+        int[][] dp = new int[n+1][total];
+        int[][] rowValid = new int[total][total];
+        List<Integer> good = new ArrayList<>();
+        List<Integer>[] pattern = new ArrayList[total];
+        for (int i = 0; i < total; i++) pattern[i] = new ArrayList<>();
+        for (int i = 0; i < total; i++) {
+            int val = i, valid = 1;
+            for (int j = 0; j < m; j++) {
+                pattern[i].add(val % 3);
+                val /= 3;
+            }
+            for (int j = 1; j < m; j++) if (pattern[i].get(j).equals(pattern[i].get(j-1))) valid = 0;
+            if (valid == 1) good.add(i);
+        }
+        for (int i : good) dp[1][i] = 1;
+        for (int i : good) {
+            for (int j : good) {
+                rowValid[i][j] = 1;
+                for (int k = 0; k < m; k++) if (pattern[i].get(k).equals(pattern[j].get(k))) rowValid[i][j] = 0;
+            }
+        }
+        for (int col = 2; col <= n; col++) {
+            for (int i : good) {
+                long sum = 0;
+                for (int j : good) if (rowValid[i][j] == 1) sum += dp[col-1][j];
+                dp[col][i] = (int)(sum % mod);
+            }
+        }
+        long ans = 0;
+        for (int i = 0; i < total; i++) ans += dp[n][i];
+        return (int)(ans % mod);
+    }
+}