java: add “1155. Number of Dice Rolls With Target Sum”

Signed-off-by: Matej Focko <me@mfocko.xyz>

java/number-of-dice-rolls-with-target-sum.java

@@ -0,0 +1,28 @@
+class Solution {
+    private static final long MOD = 1000000007;
+
+    public int numRollsToTarget(int n, int k, int target) {
+        // out of bounds
+        if (n > target || target > n * k) {
+            return 0;
+        }
+
+        long[][] dp = new long[n + 1][target + 1];
+        dp[0][0] = 1;
+
+        for (int toss = 1; toss <= n; ++toss) {
+            for (
+                int sumIdx = toss, maxSumIdx = Math.min(target, toss * k);
+                sumIdx <= maxSumIdx;
+                ++sumIdx
+            ) {
+                for (int f = 1; f <= Math.min(k, sumIdx); ++f) {
+                    dp[toss][sumIdx] = (dp[toss][sumIdx] + dp[toss - 1][sumIdx - f]) % MOD;
+                }
+            }
+        }
+
+        return (int) dp[n][target];
+    }
+}
+