time_based_key_value_store_981: solved

Author: austingebauer

time_based_key_value_store_981/README.md

@@ -0,0 +1,3 @@
+# 981. Time Based Key-Value Store
+
+https://leetcode.com/problems/time-based-key-value-store/description/

time_based_key_value_store_981/solution.go

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+package time_based_key_value_store_981
+
+import "sort"
+
+type entry struct {
+	value     string
+	timestamp int
+}
+
+type TimeMap struct {
+	m map[string][]*entry
+}
+
+func Constructor() TimeMap {
+	return TimeMap{
+		m: make(map[string][]*entry),
+	}
+}
+
+func (m *TimeMap) Set(key string, value string, timestamp int) {
+	entries, ok := m.m[key]
+	if !ok {
+		entries = make([]*entry, 0)
+	}
+
+	// perform a binary search for the sorted insertion point (timestamp asc)
+	index := sort.Search(len(entries), func(i int) bool {
+		return entries[i].timestamp > timestamp
+	})
+
+	// insert the new entry at the sorted insertion point
+	newEntry := &entry{value: value, timestamp: timestamp}
+	if index == len(entries) {
+		entries = append(entries, newEntry)
+	} else {
+		// perform a copy-shift insert
+		entries = append(entries, nil) // make space
+		copy(entries[index+1:], entries[index:])
+		entries[index] = newEntry
+	}
+
+	m.m[key] = entries
+}
+
+func (m *TimeMap) Get(key string, timestamp int) string {
+	entries, ok := m.m[key]
+	if !ok {
+		return ""
+	}
+
+	// Find the first entry where the timestamp is greater. This means
+	// the one right behind it is our entry to return. 
+	index := sort.Search(len(entries), func(i int) bool {
+		return entries[i].timestamp > timestamp
+	})
+	if index == 0 {
+		return ""
+	}
+
+	return entries[index-1].value
+}

time_based_key_value_store_981/solution_test.go

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+package time_based_key_value_store_981
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestKV(t *testing.T) {
+	kv := Constructor()
+	kv.Set("foo", "bar", 1)
+	kv.Set("foo", "baz", 4)
+	assert.Equal(t, "", kv.Get("foo", 0))
+	assert.Equal(t, "bar", kv.Get("foo", 3))
+	assert.Equal(t, "bar", kv.Get("foo", 2))
+	assert.Equal(t, "baz", kv.Get("foo", 4))
+	assert.Equal(t, "baz", kv.Get("foo", 6))
+}