go-05-lru-cache

[
  {
    "total": 10,
    "answer": "```go\npackage challenge\n\ntype LRUCache[K comparable, V any] struct {\n    capacity int\n    items  map[K]*listNode[K, V]\n    list   *doublyLinkedList[K, V]\n}\n\ntype listNode[K comparable, V any] struct {\n    key   K\n    value V\n    prev  *listNode[K, V]\n    next  *listNode[K, V]\n}\n\ntype doublyLinkedList[K comparable, V any] struct {\n    head *listNode[K, V]\n    tail *listNode[K, V]\n}\n\nfunc (l *doublyLinkedList[K, V]) pushBack(node *listNode[K, V]) {\n    if l.tail == nil {\n        l.head = node\n        l.tail = node\n    } else {\n        l.tail.next = node\n        node.prev = l.tail\n        l.tail = node\n    }\n}\n\nfunc (l *doublyLinkedList[K, V]) remove(node *listNode[K, V]) {\n    if node.prev != nil {\n        node.prev.next = node.next\n    } else {\n        l.head = node.next\n    }\n    \n    if node.next != nil {\n        node.next.prev = node.prev\n    } else {\n        l.tail = node.prev\n    }\n}\n\nfunc (l *doublyLinkedList[K, V]) popFront() *listNode[K, V] {\n    if l.head == nil {\n        return nil\n    }\n    \n    node := l.head\n    l.head = node.next\n    \n    if l.head != nil {\n        l.head.prev = nil\n    } else {\n        l.tail = nil\n    }\n    \n    return node\n}\n\nfunc NewLRUCache[K comparable, V any](capacity int) *LRUCache[K, V] {\n    if capacity <= 0 {\n        capacity = 0\n    }\n    \n    return &LRUCache[K, V]{\n        capacity: capacity,\n        items:    make(map[K]*listNode[K, V]),\n        list:     &doublyLinkedList[K, V]{},\n    }\n}\n\nfunc (c *LRUCache[K, V]) Get(key K) (V, bool) {\n    node, exists := c.items[key]\n    if !exists {\n        var zero V\n        return zero, false\n    }\n    \n    // Move to end (most recently used)\n    c.list.remove(node)\n    c.list.pushBack(node)\n    \n    return node.value, true\n}\n\nfunc (c *LRUCache[K, V]) Put(key K, value V) {\n    node, exists := c.items[key]\n    if exists {\n        // Update existing\n        node.value = value\n        c.list.remove(node)\n        c.list.pushBack(node)\n        return\n    }\n    \n    // New entry\n    newNode := &listNode[K, V]{\n        key:   key,\n        value:   value,\n    }\n    \n    if len(c.items) >= c.capacity {\n        // Evict least recently used\n        lru := c.list.popFront()\n        if lru != nil {\n            delete(c.items, lru.key)\n        }\n    }\n    \n    c.list.pushBack(newNode)\n    c.items[key] = newNode\n}\n\nfunc (c *LRUCache[K, V]) Len() int {\n    return len(c.items)\n}\n```",
    "passed": 9,
    "test_error": "06-30T06:25:49.634576175+02:00\",\"Action\":\"output\",\"Package\":\"challenge\",\"Test\":\"TestLRUCapacityOne\",\"Output\":\"--- PASS: TestLRUCapacityOne (0.00s)\\n\"}\n{\"Time\":\"2026-06-30T06:25:49.634577685+02:00\",\"Action\":\"pass\",\"Package\":\"challenge\",\"Test\":\"TestLRUCapacityOne\",\"Elapsed\":0}\n{\"Time\":\"2026-06-30T06:25:49.634579175+02:00\",\"Action\":\"run\",\"Package\":\"challenge\",\"Test\":\"TestLRUZeroCapacity\"}\n{\"Time\":\"2026-06-30T06:25:49.634581465+02:00\",\"Action\":\"output\",\"Package\":\"challenge\",\"Test\":\"TestLRUZeroCapacity\",\"Output\":\"=== RUN   TestLRUZeroCapacity\\n\"}\n{\"Time\":\"2026-06-30T06:25:49.634582965+02:00\",\"Action\":\"output\",\"Package\":\"challenge\",\"Test\":\"TestLRUZeroCapacity\",\"Output\":\"    solution_test.go:118: zero-capacity cache must store nothing\\n\"}\n{\"Time\":\"2026-06-30T06:25:49.634585855+02:00\",\"Action\":\"output\",\"Package\":\"challenge\",\"Test\":\"TestLRUZeroCapacity\",\"Output\":\"--- FAIL: TestLRUZeroCapacity (0.00s)\\n\"}\n{\"Time\":\"2026-06-30T06:25:49.634587205+02:00\",\"Action\":\"fail\",\"Package\":\"challenge\",\"Test\":\"TestLRUZeroCapacity\",\"Elapsed\":0}\n{\"Time\":\"2026-06-30T06:25:49.634588835+02:00\",\"Action\":\"run\",\"Package\":\"challenge\",\"Test\":\"TestLRUStringValues\"}\n{\"Time\":\"2026-06-30T06:25:49.634590325+02:00\",\"Action\":\"output\",\"Package\":\"challenge\",\"Test\":\"TestLRUStringValues\",\"Output\":\"=== RUN   TestLRUStringValues\\n\"}\n{\"Time\":\"2026-06-30T06:25:49.634592555+02:00\",\"Action\":\"output\",\"Package\":\"challenge\",\"Test\":\"TestLRUStringValues\",\"Output\":\"--- PASS: TestLRUStringValues (0.00s)\\n\"}\n{\"Time\":\"2026-06-30T06:25:49.634593935+02:00\",\"Action\":\"pass\",\"Package\":\"challenge\",\"Test\":\"TestLRUStringValues\",\"Elapsed\":0}\n{\"Time\":\"2026-06-30T06:25:49.634595315+02:00\",\"Action\":\"run\",\"Package\":\"challenge\",\"Test\":\"TestLRUEvictionChain\"}\n{\"Time\":\"2026-06-30T06:25:49.634596555+02:00\",\"Action\":\"output\",\"Package\":\"challenge\",\"Test\":\"TestLRUEvictionChain\",\"Output\":\"=== RUN   TestLRUEvictionChain\\n\"}\n{\"Time\":\"2026-06-30T06:25:49.634599865+02:00\",\"Action\":\"output\",\"Package\":\"challenge\",\"Test\":\"TestLRUEvictionChain\",\"Output\":\"--- PASS: TestLRUEvictionChain (0.00s)\\n\"}\n{\"Time\":\"2026-06-30T06:25:49.634601365+02:00\",\"Action\":\"pass\",\"Package\":\"challenge\",\"Test\":\"TestLRUEvictionChain\",\"Elapsed\":0}\n{\"Time\":\"2026-06-30T06:25:49.634602975+02:00\",\"Action\":\"output\",\"Package\":\"challenge\",\"Output\":\"FAIL\\n\"}\n{\"Time\":\"2026-06-30T06:25:49.634777786+02:00\",\"Action\":\"output\",\"Package\":\"challenge\",\"Output\":\"FAIL\\tchallenge\\t0.001s\\n\"}\n{\"Time\":\"2026-06-30T06:25:49.634795026+02:00\",\"Action\":\"fail\",\"Package\":\"challenge\",\"Elapsed\":0.001}"
  },
  {
    "total": 10,
    "answer": "Looking at the failing test, it seems like when capacity is 0, the cache should store nothing. Let me examine my implementation more carefully.\n\nThe issue is in how I handle zero capacity. When `capacity <= 0`, I set it to 0, but I'm not properly handling the case where we try to insert items into a zero-capacity cache. In a zero-capacity cache, no items should ever be stored, even if we call Put.\n\nLet me fix this:\n\n```go\npackage challenge\n\ntype LRUCache[K comparable, V any] struct {\n    capacity int\n    items  map[K]*listNode[K, V]\n    list   *doublyLinkedList[K, V]\n}\n\ntype listNode[K comparable, V any] struct {\n    key   K\n    value V\n    prev  *listNode[K, V]\n    next  *listNode[K, V]\n}\n\ntype doublyLinkedList[K comparable, V any] struct {\n    head *listNode[K, V]\n    tail *listNode[K, V]\n}\n\nfunc (l *doublyLinkedList[K, V]) pushBack(node *listNode[K, V]) {\n    if l.tail == nil {\n        l.head = node\n        l.tail = node\n    } else {\n        l.tail.next = node\n        node.prev = l.tail\n        l.tail = node\n    }\n}\n\nfunc (l *doublyLinkedList[K, V]) remove(node *listNode[K, V]) {\n    if node.prev != nil {\n        node.prev.next = node.next\n    } else {\n        l.head = node.next\n    }\n    \n    if node.next != nil {\n        node.next.prev = node.prev\n    } else {\n        l.tail = node.prev\n    }\n}\n\nfunc (l *doublyLinkedList[K, V]) popFront() *listNode[K, V] {\n    if l.head == nil {\n        return nil\n    }\n    \n    node := l.head\n    l.head = node.next\n    \n    if l.head != nil {\n        l.head.prev = nil\n    } else {\n        l.tail = nil\n    }\n    \n    return node\n}\n\nfunc NewLRUCache[K comparable, V any](capacity int) *LRUCache[K, V] {\n    if capacity <= 0 {\n        capacity = 0\n    }\n    \n    return &LRUCache[K, V]{\n        capacity: capacity,\n        items:    make(map[K]*listNode[K, V]),\n        list:   &doublyLinkedList[K, V]{},\n    }\n}\n\nfunc (c *LRUCache[K, V]) Get(key K) (V, bool) {\n    if c.capacity == 0 {\n        var zero V\n        return zero, false\n    }\n    \n    node, exists := c.items[key]\n    if !exists {\n        var zero V\n        return zero, false\n    }\n    \n    // Move to end (most recently used)\n    c.list.remove(node)\n    c.list.pushBack(node)\n    \n    return node.value, true\n}\n\nfunc (c *LRUCache[K, V]) Put(key K, value V) {\n    if c.capacity == 0 {\n        return\n    }\n    \n    node, exists := c.items[key]\n    if exists {\n        // Update existing\n        node.value = value\n        c.list.remove(node)\n        c.list.pushBack(node)\n        return\n    }\n    \n    // New entry\n    newNode := &listNode[K, V]{\n        key:   key,\n        value: value,\n    }\n    \n    if len(c.items) >= c.capacity {\n        // Evict least recently used\n        lru := c.list.popFront()\n        if lru != nil {\n            delete(c.items, lru.key)\n        }\n    }\n    \n    c.list.pushBack(newNode)\n    c.items[key] = newNode\n}\n\nfunc (c *LRUCache[K, V]) Len() int {\n    return len(c.items)\n}\n```",
    "passed": 10,
    "test_error": ""
  }
]

You are an expert programmer. Solve the task exactly as specified. Output your solution as fenced code blocks using the required file name(s) and the exact function/type signatures requested. Prefer correctness; do not include prose outside code unless asked.