covert slice of ints into zig_zag

Author: danrusei

README.md

@@ -107,7 +107,7 @@ WIP, the descriptions of the below `unsolved yet` problems can be found in the [
 - [x] [Reverse an array without affecting special characters](https://github.com/danrusei/algorithms_with_Go/tree/main/strings/reverse_alpha)
 - [] All Possible Palindromic Partitions
 - [] Count triplets with sum smaller than a given value
-- [] Convert array into Zig-Zag fashion
+- [x] [Convert array into Zig-Zag fashion](https://github.com/danrusei/algorithms_with_Go/tree/main/strings/zig_zag)
 - [] Generate all possible sorted arrays from alternate elements of two given sorted arrays
 - [] Pythagorean Triplet in an array
 - [x] [Length of the largest subarray with contiguous elements](https://github.com/danrusei/algorithms_with_Go/tree/main/strings/largest_subarray)

strings/zig_zag/README.md

@@ -0,0 +1,35 @@
+# Convert array into Zig-Zag fashion
+
+Source: [GeeksforGeeks](https://www.geeksforgeeks.org/convert-array-into-zig-zag-fashion/amp/)
+
+Given an array of DISTINCT elements, rearrange the elements of array in zig-zag fashion in O(n) time. The converted array should be in form a < b > c < d > e < f.
+
+## Example
+
+```bash
+Input: arr[] = {4, 3, 7, 8, 6, 2, 1} 
+Output: arr[] = {3, 7, 4, 8, 2, 6, 1}
+
+Input: arr[] = {1, 4, 3, 2} 
+Output: arr[] = {1, 4, 2, 3}
+```
+
+## Algorithm
+
+* create a flag to denote the "<" or ">"
+* if two consecutive numbers do not have the expected relationship, then swap the elements
+
+## Result
+
+```bash
+$ go test -v
+=== RUN   TestReverse
+=== RUN   TestReverse/first_10
+=== RUN   TestReverse/7_values
+=== RUN   TestReverse/4_values
+--- PASS: TestReverse (0.00s)
+    --- PASS: TestReverse/first_10 (0.00s)
+    --- PASS: TestReverse/7_values (0.00s)
+    --- PASS: TestReverse/4_values (0.00s)
+PASS
+```

strings/zig_zag/test_cases.go

@@ -0,0 +1,23 @@
+package zigzag
+
+var testcases = []struct {
+	name   string
+	input  []int
+	output []int
+}{
+	{
+		name:   "first_10",
+		input:  []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10},
+		output: []int{1, 3, 2, 5, 4, 7, 6, 9, 8, 10},
+	},
+	{
+		name:   "7_values",
+		input:  []int{4, 3, 7, 8, 6, 2, 1},
+		output: []int{3, 7, 4, 8, 2, 6, 1},
+	},
+	{
+		name:   "4_values",
+		input:  []int{1, 4, 3, 2},
+		output: []int{1, 4, 2, 3},
+	},
+}

strings/zig_zag/zigzag.go

@@ -0,0 +1,24 @@
+package zigzag
+
+func zigzag(input []int) {
+
+	// if `less` is true indicate "<", else ">"
+	// initially is true as we start with "<"
+	// a < b > c < d > e < f
+	less := true
+
+	for i := 0; i <= len(input)-2; i++ {
+		if less {
+			if input[i] > input[i+1] {
+				input[i], input[i+1] = input[i+1], input[i]
+			}
+		} else {
+			if input[i] < input[i+1] {
+				input[i], input[i+1] = input[i+1], input[i]
+			}
+		}
+
+		// change flag to false, as we should operate on oposite signo
+		less = !less
+	}
+}

strings/zig_zag/zigzag_test.go

@@ -0,0 +1,17 @@
+package zigzag
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestReverse(t *testing.T) {
+	for _, tc := range testcases {
+		t.Run(tc.name, func(t *testing.T) {
+			zigzag(tc.input)
+			if !reflect.DeepEqual(tc.input, tc.output) {
+				t.Errorf("Expected: %d, got: %d", tc.output, tc.input)
+			}
+		})
+	}
+}