Discussion on: Daily Challenge #60 - Find the Missing Letter

package find

// MissingLetter indicates what the missing character is in a ordered sequence of characters
func MissingLetter(chars []rune) rune {
    var last int

    for _, r := range chars {
        if last != 0 && int(r)-last > 1 {
            return rune(r - 1)
        }
        last = int(r)
    }

    return rune(last)
}

package find

import "testing"

type testCase struct {
    description string
    input       []rune
    expected    rune
}

func TestMissingLetter(t *testing.T) {
    testCases := []testCase{
        {
            "two characters",
            []rune{'A', 'C'},
            'B',
        },
        {
            "dev-to example one",
            []rune{'a', 'b', 'c', 'd', 'f'},
            'e',
        },
        {
            "dev-to example two",
            []rune{'O', 'Q', 'R', 'S'},
            'P',
        },
    }

    for _, test := range testCases {
        if result := MissingLetter(test.input); result != test.expected {
            t.Fatalf("FAIL: %s - MissingLetter(%+v): %v - expected %v", test.description, test.input, result, test.expected)
        }
        t.Logf("PASS: %s", test.description)
    }
}