Solution.kt

package g0201_0300.s0228_summary_ranges

// #Easy #Array #Top_Interview_150_Intervals #2022_10_26_Time_169_ms_(91.89%)_Space_34_MB_(95.95%)

class Solution {
    fun summaryRanges(nums: IntArray): List<String> {
        val ranges: MutableList<String> = ArrayList()
        if (nums.size == 0) {
            return ranges
        }
        // size of array
        val n = nums.size
        // start of range
        var a = nums[0]
        // end of range
        var b = a
        val strB = StringBuilder()
        for (i in 1 until n) {
            // we need to make a decision if the next element
            // will expand the range
            // i starts at 1, not 0, because 1 is the next
            // candidate for expanding the range
            if (nums[i] != b + 1) {
                // only when our next element does not expand the range
                // do we add the range a->b to our list of ranges
                strB.append(a)
                if (a != b) {
                    strB.append("->").append(b)
                }
                ranges.add(strB.toString())
                // since nums[i] is not accounted for by our range a->b
                // because nums[i] is not b+1, we need to set a and b
                // to this new range start point of bigger than b+1
                // maybe it is b+2? b+3? b+4? all we know is it is not b+1
                a = nums[i]
                b = a
                // Reset string builder
                strB.setLength(0)
            } else {
                // if the next element expands our range we do so
                b++
            }
        }
        // the only range that is not accounted for at this point is the last range
        // if our a and b are not equal then we add the range accordingly
        strB.append(a)
        if (a != b) {
            strB.append("->").append(b)
        }
        ranges.add(strB.toString())
        return ranges
    }
}