SummaryRanges.java

package Leetcode;

import java.util.ArrayList;
import java.util.List;

/**
 * @author kalpak
 *
 * You are given a sorted unique integer array nums.
 *
 * 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"
 *
 *
 * Example 3:
 * Input: nums = []
 * Output: []
 *
 *
 * Example 4:
 * Input: nums = [-1]
 * Output: ["-1"]
 *
 *
 * Example 5:
 * Input: nums = [0]
 * Output: ["0"]
 *
 *
 * Constraints:
 *
 * 0 <= nums.length <= 20
 * -2^31 <= nums[i] <= 2^31 - 1.
 * All the values of nums are unique.
 * nums is sorted in ascending order.
 *
 */

public class SummaryRanges {
    public static List<String> summaryRanges(int[] nums) {
        List<String> result = new ArrayList<>();

        for(int i = 0, j = 0; j < nums.length; j++) {
            while(j + 1 < nums.length && nums[j+1] == nums[j] + 1)
                j++;
            //
            if(i == j)
                result.add(nums[i] + "");
            else
                result.add(nums[i] + "->" + nums[j]);

            i=j+1;
        }
        return result;
    }

    public static void main(String[] args) {
        int[] nums = new int[]{0,2,3,4,6,8,9};
        System.out.println(summaryRanges(nums));
    }
}