Add solution for cw-grasshopper-summation and cw-returning-strings

cw-grasshopper-summation/README.md

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+# Grasshopper - Summation
+
+Write a program that finds the summation of every number from `1` to num. The number will always be a positive integer greater than `0`. Your function only needs to return the result, what is shown between parentheses in the example below is how you reach that result and it's not part of it, see the sample tests.
+
+For example (Input -> Output):
+`2 -> 3 (1 + 2)`
+`8 -> 36 (1 + 2 + 3 + 4 + 5 + 6 + 7 + 8)`

cw-grasshopper-summation/go.mod

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+module github.com/skosovsky/algo/cw-grasshopper-summation
+go 1.21.5

cw-grasshopper-summation/main.go

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+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	fmt.Println(summation(213)) //nolint:gomnd
+}
+
+func summation(n int) int {
+	var sum int
+
+	for i := n; i > 0; i-- {
+		sum += i
+	}
+
+	return sum
+}
+
+func summationClever(n int) int {
+	return n * (n + 1) / 2
+}

cw-grasshopper-summation/main_test.go

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+package main
+
+import "testing"
+
+func Test_summation(t *testing.T) {
+	type args struct {
+		n int
+	}
+	tests := []struct {
+		name string
+		args args
+		want int
+	}{
+		{
+			name: "Example 1",
+			args: args{2},
+			want: 3,
+		},
+		{
+			name: "Example 2",
+			args: args{1},
+			want: 1,
+		},
+		{
+			name: "Example 3",
+			args: args{8},
+			want: 36,
+		},
+		{
+			name: "Example 4",
+			args: args{22},
+			want: 253,
+		},
+		{
+			name: "Example 5",
+			args: args{100},
+			want: 5050,
+		},
+		{
+			name: "Example 6",
+			args: args{213},
+			want: 22791,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := summation(tt.args.n); got != tt.want {
+				t.Errorf("summation() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}

cw-returning-strings/README.md

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+# Returning Strings
+
+Make a function that will return a greeting statement that uses an input; your program should return, `"Hello, <name> how are you doing today?"`.
+
+[Make sure you type the exact thing I wrote or the program may not execute properly]

cw-returning-strings/go.mod

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+module github.com/skosovsky/algo/cw-returning-strings
+go 1.21.5

cw-returning-strings/main.go

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+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	fmt.Println(greet("Bob"))
+}
+
+func greet(name string) string {
+	hello := fmt.Sprintf("Hello, %s how are you doing today?", name)
+	return hello
+}