#1 3.5 Sort Stack implementation

README.md

@@ -43,7 +43,7 @@ Solving programming questions from ["Cracking the Coding Interview 6th Edition"]
 | 3.2 | [Stack Min][43]        | [tests][44] |   ✓    |
 | 3.3 | [Stack of Plates][45]  | [tests][46] |   ✓    |
 | 3.4 | [Queue via Stacks][47] | [tests][48] |   ✓    |
-| 3.5 | Sort Stack             |    tests    |        |
+| 3.5 | [Sort Stack][49]       | [tests][50] |   ✓    |
 | 3.6 | Animal Shelter         |    tests    |        |
 
 [1]:  ch01/01_is_unique.go
@@ -94,3 +94,5 @@ Solving programming questions from ["Cracking the Coding Interview 6th Edition"]
 [46]:  ch03/03_stack_of_plates_test.go
 [47]:  ch03/04_my_queue.go
 [48]:  ch03/04_my_queue_test.go
+[49]:  ch03/05_sort_stack.go
+[50]:  ch03/05_sort_stack_test.go

ch03/05_sort_stack.go

@@ -0,0 +1,31 @@
+package ch03
+
+// Sort stack in ascending order (min values on top)
+// Use temporary stack to sort values in descending
+// order. Then reverse it into original stack.
+func Sort(stack *Stack) {
+	sorted := new(Stack)
+
+	// fill in sorted stack in descending order
+	for !stack.IsEmpty() {
+		tmp, _ := stack.Pop()
+
+		for !sorted.IsEmpty() {
+			top, _ := sorted.Peek()
+			if top < tmp {
+				break
+			}
+
+			top, _ = sorted.Pop()
+			stack.Push(top)
+		}
+
+		sorted.Push(tmp)
+	}
+
+	// reverse sorted stack
+	for !sorted.IsEmpty() {
+		top, _ := sorted.Pop()
+		stack.Push(top)
+	}
+}

ch03/05_sort_stack_test.go

@@ -0,0 +1,41 @@
+package ch03
+
+import "testing"
+
+func TestSort(t *testing.T) {
+	type args struct {
+		stack  *Stack
+		values []int
+	}
+	tests := []struct {
+		name string
+		args args
+		want []int
+	}{
+		{
+			name: "sorts random stack",
+			args: args{stack: new(Stack), values: []int{1, 2, 3, 4, 10}},
+			want: []int{1, 2, 3, 4, 10},
+		},
+		{
+			name: "sorts a stack that already sorted",
+			args: args{stack: new(Stack), values: []int{5, 4, 3, 2, 1}},
+			want: []int{1, 2, 3, 4, 5},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			stack := tt.args.stack
+			for _, v := range tt.args.values {
+				stack.Push(v)
+			}
+			Sort(stack)
+			for _, want := range tt.want {
+				got, _ := stack.Pop()
+				if got != want {
+					t.Errorf("Sorted stack Pop() got = %v, want %v", got, want)
+				}
+			}
+		})
+	}
+}