Summary range

Author: Tushar Roy

src/com/interview/array/SummaryRanges.java

@@ -0,0 +1,51 @@
+package com.interview.array;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * Date 10/19/2016
+ * @author Tushar Roy
+ *
+ * Given a sorted integer array without duplicates, return the summary of its ranges.
+ * For example, given [0,1,2,4,5,7], return ["0->2","4->5","7"].
+ *
+ * Solution -
+ * Just check if num[i] + 1 != num[i + 1]. If its not equal means you need to add previous range to result
+ * and start a new range.
+ * 
+ * Time complexity O(n)
+ *
+ * https://leetcode.com/problems/summary-ranges/
+ */
+public class SummaryRanges {
+    public List<String> summaryRanges(int[] nums) {
+        if (nums.length == 0) {
+            return Collections.EMPTY_LIST;
+        }
+        if (nums.length == 1) {
+            return Collections.singletonList(String.valueOf(nums[0]));
+        }
+        int start = 0;
+        List<String> result = new ArrayList<>();
+        for (int i = 0; i < nums.length - 1; i++) {
+            if ((nums[i] + 1) != nums[i + 1]) {
+                result.add(makeRange(nums[start], nums[i]));
+                start = i + 1;
+            }
+        }
+        if ((nums[nums.length - 2] + 1) != nums[nums.length - 1]) {
+            start = nums.length - 1;
+        }
+        result.add(makeRange(nums[start], nums[nums.length - 1]));
+        return result;
+    }
+
+    private String makeRange(int a, int b) {
+        if (a == b) {
+            return String.valueOf(a);
+        }
+        return a + "->" + b;
+    }
+}