package main

import (
	"fmt"
	"runtime"
	"time"
)

// noPrealloc 未预分配容量，频繁扩容
func noPrealloc() {
	var data []int
	for i := 0; i < 100000; i++ {
		data = append(data, i)
	}
}

// withPrealloc 预分配容量，无扩容
func withPrealloc() {
	data := make([]int, 0, 100000) // 预分配容量100000
	for i := 0; i < 100000; i++ {
		data = append(data, i)
	}
}

func main() {
	var stats runtime.MemStats

	// 测试未预分配
	runtime.GC()
	start := time.Now()
	noPrealloc()
	dur1 := time.Since(start)
	runtime.ReadMemStats(&stats)
	fmt.Printf("未预分配：耗时%v，堆分配%d KB，GC次数%d\n", dur1, stats.HeapAlloc/1024, stats.NumGC)

	// 测试预分配
	runtime.GC()
	start = time.Now()
	withPrealloc()
	dur2 := time.Since(start)
	runtime.ReadMemStats(&stats)
	fmt.Printf("预分配：耗时%v，堆分配%d KB，GC次数%d\n", dur2, stats.HeapAlloc/1024, stats.NumGC)
}