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day 127: sum reversed linked list digits
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package day127 | ||
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// RevLLNum represents a reversed linked list of digits. | ||
type RevLLNum struct { | ||
Digit int | ||
Next *RevLLNum | ||
} | ||
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// SumRevLLNum returns the sum of two RevLLNum as a new RevLLNum. | ||
func SumRevLLNum(first, second *RevLLNum) *RevLLNum { | ||
var carryOne bool | ||
result := &RevLLNum{} | ||
current := result | ||
for first != nil || second != nil { | ||
current.Next = &RevLLNum{} | ||
current = current.Next | ||
var sum int | ||
if first == nil { | ||
sum = second.Digit | ||
second = second.Next | ||
} else if second == nil { | ||
sum = first.Digit | ||
first = first.Next | ||
} else { | ||
sum = first.Digit + second.Digit | ||
first = first.Next | ||
second = second.Next | ||
} | ||
if carryOne { | ||
sum++ | ||
} | ||
carryOne = sum > 9 | ||
current.Digit = sum % 10 | ||
} | ||
if carryOne { | ||
current.Next = &RevLLNum{1, nil} | ||
} | ||
return result.Next | ||
} |
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package day127 | ||
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import ( | ||
"strconv" | ||
"strings" | ||
"testing" | ||
) | ||
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var testcases = []struct { | ||
first, second, sum *RevLLNum | ||
}{ | ||
{&RevLLNum{9, &RevLLNum{9, nil}}, | ||
&RevLLNum{5, &RevLLNum{2, nil}}, | ||
&RevLLNum{4, &RevLLNum{2, &RevLLNum{1, nil}}}}, | ||
{&RevLLNum{9, &RevLLNum{9, nil}}, | ||
nil, | ||
&RevLLNum{9, &RevLLNum{9, nil}}}, | ||
{nil, | ||
&RevLLNum{9, &RevLLNum{9, nil}}, | ||
&RevLLNum{9, &RevLLNum{9, nil}}}, | ||
{&RevLLNum{9, &RevLLNum{9, &RevLLNum{9, &RevLLNum{9, nil}}}}, | ||
&RevLLNum{1, nil}, | ||
&RevLLNum{0, &RevLLNum{0, &RevLLNum{0, &RevLLNum{0, &RevLLNum{1, nil}}}}}}, | ||
} | ||
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func TestSumRevLLNum(t *testing.T) { | ||
t.Parallel() | ||
for tcid, tc := range testcases { | ||
if result := SumRevLLNum(tc.first, tc.second); !equal(result, tc.sum) { | ||
t.Errorf("TCID%d does not match expected. Got %v expected %v", | ||
tcid, String(result), String(tc.sum)) | ||
} | ||
} | ||
} | ||
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func BenchmarkSumRevLLNum(b *testing.B) { | ||
for i := 0; i < b.N; i++ { | ||
for _, tc := range testcases { | ||
SumRevLLNum(tc.first, tc.second) | ||
} | ||
} | ||
} | ||
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func equal(a, b *RevLLNum) bool { | ||
if a == nil && b == nil { | ||
return true | ||
} else if a == nil && b != nil { | ||
return false | ||
} else if a != nil && b == nil { | ||
return false | ||
} | ||
for a != nil && b != nil { | ||
if a.Digit != b.Digit { | ||
return false | ||
} | ||
a = a.Next | ||
b = b.Next | ||
} | ||
return a == b | ||
} | ||
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func String(a *RevLLNum) string { | ||
var sb strings.Builder | ||
for a != nil { | ||
sb.WriteString(strconv.Itoa(a.Digit)) | ||
a = a.Next | ||
} | ||
return sb.String() | ||
} |