Add the solution for LC #3551

Author: rayworks

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

@@ -0,0 +1,56 @@
+package org.sean.graph;
+
+import java.util.Arrays;
+
+/***
+ * 3551. Minimum Swaps to Sort by Digit Sum
+ */
+public class MinSwapsCounter {
+    public int minSwaps(int[] nums) {
+        int len = nums.length;
+
+        // <val, sum, pos>
+        int[][] elements = new int[len][3];
+        for (int i = 0; i < len; i++) {
+            elements[i][0] = nums[i];
+
+            int elem = nums[i];
+            int sum = 0;
+            while (elem > 0) {
+                sum += elem % 10;
+                elem /= 10;
+            }
+            elements[i][1] = sum;
+            elements[i][2] = i;
+        }
+
+        int[] actualIndexes = new int[len];
+        Arrays.sort(elements, (o1, o2) -> {
+            if (o1[1] == o2[1]) { // sort by the min value
+                return Integer.compare(o1[0], o2[0]);
+            } else {
+                return Integer.compare(o1[1], o2[1]);
+            }
+        });
+        for (int i = 0; i < len; i++) {
+            actualIndexes[i] = elements[i][2];
+        }
+
+        // System.out.println(Arrays.toString(actualIndexes));
+
+        // Simplify the problem as sorting the array actualIndexes by swapping 2 elements
+        // n - numOfCircles
+        boolean[] visited = new boolean[len];
+        int res = len;
+        for (int i = 0; i < len; i++) {
+            if (visited[i]) continue;
+            int j = i;
+            while (!visited[j]) {
+                visited[j] = true;
+                j = actualIndexes[j];
+            }
+            res--;
+        }
+        return res;
+    }
+}

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

@@ -0,0 +1,22 @@
+package org.sean.graph;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class MinSwapsCounterTest {
+
+    private MinSwapsCounter counter;
+
+    @Before
+    public void setUp() throws Exception {
+        counter = new MinSwapsCounter();
+    }
+
+    @Test
+    public void minSwaps() {
+        int cnt = counter.minSwaps(new int[]{18, 43, 34, 16});
+        assertEquals(2, cnt);
+    }
+}