add missing ranges problem

leetcode/missing_ranges_test.go

@@ -0,0 +1,118 @@
+/*
+Problem:
+- Given a sorted integer array where the range of elements are [0, 99] inclusive,
+  return its missing ranges.
+
+Example:
+- Input: []int{0, 1, 6, 16, 66, 99}
+  Output: []string{"2-5", "7-15", "17-65", "67-98"}
+- Input: []int{6, 16, 66}
+  Output: []string{"0-5", "7-15", "17-65", "67-99"}
+
+Approach:
+- Keep two pointers where one is ahead of the other by 1 index.
+- Iterate through the list, calculate the difference of two consecutive numbers
+  in the list at each step and append it to a new list.
+
+Solution:
+- Initialize a list of string as an output, two pointers where one is ahead of
+  the other by 1.
+- While p2 is less than the length of the input list, check if the difference
+  between two current numbers are greater or equal to 2.
+- If so, add it.
+- Otherwise, no need to add it because they are consecutive numbers already so
+  there is no range to get.
+- Make sure to check the edge case where the first value in the input list is
+  either 0 or 99.
+
+Cost:
+- O(n) time, O(m) space, where m < n and n is the size of the input.
+*/
+
+package leetcode
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/hoanhan101/algo/common"
+)
+
+func TestFindMissingRanges(t *testing.T) {
+	tests := []struct {
+		in       []int
+		expected []string
+	}{
+		{[]int{}, []string{}},
+		{[]int{6}, []string{"0-5", "7-99"}},
+		{[]int{0, 6}, []string{"1-5", "7-99"}},
+		{[]int{6, 99}, []string{"0-5", "7-98"}},
+		{[]int{0, 6, 99}, []string{"1-5", "7-98"}},
+		{[]int{6, 16, 66}, []string{"0-5", "7-15", "17-65", "67-99"}},
+		{[]int{0, 1, 6, 16, 66, 99}, []string{"2-5", "7-15", "17-65", "67-98"}},
+	}
+
+	for _, tt := range tests {
+		result := findMissingRanges(tt.in)
+		common.Equal(t, tt.expected, result)
+	}
+}
+
+func TestGetRange(t *testing.T) {
+	tests := []struct {
+		in1      int
+		in2      int
+		expected string
+	}{
+		{-1, 100, "0-99"},
+		{0, 99, "1-98"},
+		{1, 98, "2-97"},
+	}
+
+	for _, tt := range tests {
+		result := getRange(tt.in1, tt.in2)
+		common.Equal(t, tt.expected, result)
+	}
+}
+
+func findMissingRanges(list []int) []string {
+	// initialize a list of string as an output.
+	out := []string{}
+
+	p1 := 0
+	p2 := p1 + 1
+
+	if len(list) == 0 {
+		return out
+	}
+
+	// check edge case where the first value is not 0.
+	if list[0] != 0 {
+		out = append(out, getRange(-1, list[0]))
+	}
+
+	for p2 < len(list) {
+		// if the difference between two numbers are greater or equal to 2 then
+		// add it. otherwise, no need to add because they are consecutive
+		// numbers already so there is no range to get.
+		if list[p2]-list[p1] >= 2 {
+			out = append(out, getRange(list[p1], list[p2]))
+		}
+
+		p1++
+		p2++
+	}
+
+	// check edge case where the last value is not 99.
+	if list[len(list)-1] != 99 {
+		out = append(out, getRange(list[len(list)-1], 100))
+	}
+
+	return out
+}
+
+// getRange returns the string representation of the range between the lower
+// bound and upper bound.
+func getRange(start, end int) string {
+	return fmt.Sprintf("%v-%v", start+1, end-1)
+}