Problem
This is the advanced follow-up to Flatten a 2D Array. Practice that challenge first. Here lists may contain more lists at any depth. In C++ and C#, use the NestedValue type in the starter code. Read kind first: 0 means skip this entry, 1 means append value, and 2 means visit items recursively.
Turn a nested list into a flat list of integers. Read from left to right; whenever you reach another list, read its contents before continuing. Ignore null values (shown as None in examples) and empty lists. Preserve repeated integers and their order.
Python receives ordinary nested lists containing integers and None. C++ and C# receive a list of NestedValue objects supplied by the starter: kind 0 means null, kind 1 means integer in value, and kind 2 means a list in items. Only the field selected by kind matters. Return a plain integer list in every language.
Implement flatten_arbitrarily_nested_list(values).
Input
values: A list whose entries can be integers, null, or further lists.
Output
Return the integers in depth-first, left-to-right order. Return an empty list when there are no integers.
Constraints
The outer value is a list. At most 10,000 entries across all lists; maximum nesting depth 50. Integer leaves fit signed 64-bit. Leaves are integers or null, never strings or booleans.
Examples
Input:
values = [
1,
[
2,
None,
[3]
],
[],
4
]
Expected output:
expected = [1, 2, 3, 4]Use the NestedValue type provided in the starter code. Its fields are kind (0 = null, 1 = integer, 2 = list), value (the integer), and items (the nested list).
Input:
std::vector<NestedValue> values = {
NestedValue{1, 1, {}},
NestedValue{2, 0, {
NestedValue{1, 2, {}},
NestedValue{0, 0, {}},
NestedValue{2, 0, {
NestedValue{1, 3, {}}
}}
}},
NestedValue{2, 0, {}},
NestedValue{1, 4, {}}
};
Expected output:
std::vector<long long> expected = {1, 2, 3, 4};Use the NestedValue type provided in the starter code. Its fields are kind (0 = null, 1 = integer, 2 = list), value (the integer), and items (the nested list).
Input:
NestedValue[] values = new NestedValue[] {
new NestedValue { kind = 1, value = 1 },
new NestedValue { kind = 2, items = new NestedValue[] {
new NestedValue { kind = 1, value = 2 },
new NestedValue { kind = 0 },
new NestedValue { kind = 2, items = new NestedValue[] {
new NestedValue { kind = 1, value = 3 }
} }
} },
new NestedValue { kind = 2, items = new NestedValue[] {} },
new NestedValue { kind = 1, value = 4 }
};
Expected output:
long[] expected = new long[] {1, 2, 3, 4};Explanation
Read 1, then enter the nested list and read 2 and 3, skipping null. The empty list adds nothing; finish with 4.
Input:
values = [
None,
[],
[None]
]
Expected output:
expected = []Use the NestedValue type provided in the starter code. Its fields are kind (0 = null, 1 = integer, 2 = list), value (the integer), and items (the nested list).
Input:
std::vector<NestedValue> values = {
NestedValue{0, 0, {}},
NestedValue{2, 0, {}},
NestedValue{2, 0, {
NestedValue{0, 0, {}}
}}
};
Expected output:
std::vector<long long> expected = {};Use the NestedValue type provided in the starter code. Its fields are kind (0 = null, 1 = integer, 2 = list), value (the integer), and items (the nested list).
Input:
NestedValue[] values = new NestedValue[] {
new NestedValue { kind = 0 },
new NestedValue { kind = 2, items = new NestedValue[] {} },
new NestedValue { kind = 2, items = new NestedValue[] {
new NestedValue { kind = 0 }
} }
};
Expected output:
long[] expected = new long[] {};Explanation
Every entry is null or an empty container. No integer remains.
References
This challenge is adapted for CodeUtility. Follow the statement and constraints above.