Add a solution for LeetCode #473

Author: rayworks

src/main/java/org/sean/backtracking/StickSquare.kt

@@ -0,0 +1,47 @@
+package org.sean.backtracking
+
+import java.util.*
+
+/***
+ * 473. Matchsticks to Square
+ */
+class StickSquare {
+    private lateinit var visited: BooleanArray
+
+    private fun makesquareHelper(edges: Int, nums: IntArray, target: Int, sum: Int, pos: Int): Boolean {
+        if (edges == 4) {
+            return true
+        }
+        if (edges > 4) {
+            return false
+        }
+        if (sum == target) return makesquareHelper(edges + 1, nums, target, 0, 0)
+
+        for (i in pos until nums.size) {
+            if (visited[i]) continue
+            if (sum + nums[i] > target) continue
+
+            visited[i] = true
+            if (makesquareHelper(edges, nums, target, sum + nums[i], i + 1)) {
+                return true
+            }
+            visited[i] = false
+        }
+        return false
+    }
+
+    /***
+     * The problem is very similar to [SubsetPartition]
+     */
+    fun makesquare(matchsticks: IntArray): Boolean {
+        if (matchsticks.size < 4) return false
+        val sum = Arrays.stream(matchsticks).sum()
+        if (sum % 4 != 0) return false
+        val edgeLen = sum / 4
+        if (Arrays.stream(matchsticks).max().asInt > edgeLen) return false
+        visited = BooleanArray(matchsticks.size)
+        Arrays.sort(matchsticks)
+
+        return makesquareHelper(0, matchsticks, edgeLen, 0, 0)
+    }
+}

src/test/java/org/sean/backtracking/StickSquareTest.kt

@@ -0,0 +1,20 @@
+package org.sean.backtracking
+
+import org.junit.Before
+import org.junit.Test
+
+import org.junit.Assert.*
+
+class StickSquareTest {
+    lateinit var square: StickSquare
+
+    @Before
+    fun setUp() {
+        square = StickSquare()
+    }
+
+    @Test
+    fun makesquare() {
+        assert(square.makesquare(intArrayOf(5, 5, 5, 5, 4, 4, 4, 4, 3, 3, 3, 3)))
+    }
+}