Add soultion of SummaryRanges task

Author: andrei-punko

src/main/java/by/andd3dfx/common/SummaryRanges.java

@@ -0,0 +1,80 @@
+package by.andd3dfx.common;
+
+import java.util.ArrayList;
+import java.util.List;
+import lombok.AllArgsConstructor;
+
+/**
+ * <pre>
+ * <a href="https://leetcode.com/problems/summary-ranges/description/">Task description</a>
+ *
+ * You are given a sorted unique integer array nums.
+ *
+ * A range [a,b] is the set of all integers from a to b (inclusive).
+ *
+ * Return the smallest sorted list of ranges that cover all the numbers in the array exactly. That is, each element of nums
+ * is covered by exactly one of the ranges, and there is no integer x such that x is in one of the ranges but not in nums.
+ *
+ * Each range [a,b] in the list should be output as:
+ *     "a->b" if a != b
+ *     "a" if a == b
+ *
+ * Example 1:
+ *   Input: nums = [0,1,2,4,5,7]
+ *   Output: ["0->2","4->5","7"]
+ *   Explanation: The ranges are:
+ *   [0,2] --> "0->2"
+ *   [4,5] --> "4->5"
+ *   [7,7] --> "7"
+ *
+ * Example 2:
+ *   Input: nums = [0,2,3,4,6,8,9]
+ *   Output: ["0","2->4","6","8->9"]
+ *   Explanation: The ranges are:
+ *   [0,0] --> "0"
+ *   [2,4] --> "2->4"
+ *   [6,6] --> "6"
+ *   [8,9] --> "8->9"
+ * </pre>
+ */
+public class SummaryRanges {
+
+    public static List<String> summaryRanges(int[] nums) {
+        if (nums.length == 0) {
+            return List.of();
+        }
+
+        List<Range> ranges = new ArrayList<>();
+        Range draftRange = new Range(nums[0], nums[0]);
+        ranges.add(draftRange);
+
+        for (var value : nums) {
+            if ((value - draftRange.right) <= 1) {
+                draftRange.right = value;
+                continue;
+            }
+
+            draftRange = new Range(value, value);
+            ranges.add(draftRange);
+        }
+
+        return ranges.stream()
+            .map(Range::toString)
+            .toList();
+    }
+
+    @AllArgsConstructor
+    public static class Range {
+
+        private int left;
+        private int right;
+
+        @Override
+        public String toString() {
+            if (left == right) {
+                return String.valueOf(left);
+            }
+            return left + "->" + right;
+        }
+    }
+}

src/test/java/by/andd3dfx/common/SummaryRangesTest.java

@@ -0,0 +1,24 @@
+package by.andd3dfx.common;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.List;
+import org.junit.Test;
+
+public class SummaryRangesTest {
+
+    @Test
+    public void testSummaryRanges() {
+        assertThat(SummaryRanges.summaryRanges(new int[]{}))
+            .isEqualTo(List.of());
+
+        assertThat(SummaryRanges.summaryRanges(new int[]{0, 1, 2, 4, 5, 7}))
+            .isEqualTo(List.of("0->2", "4->5", "7"));
+
+        assertThat(SummaryRanges.summaryRanges(new int[]{0, 2, 3, 4, 6, 8, 9}))
+            .isEqualTo(List.of("0", "2->4", "6", "8->9"));
+
+        assertThat(SummaryRanges.summaryRanges(new int[]{-2147483648, 0, 2, 3, 4, 6, 8, 9}))
+            .isEqualTo(List.of("-2147483648->0", "2->4", "6", "8->9"));
+    }
+}