CPMagical CP Library

Problem solution · Go

Codeforces 1140C — Playlist

Codeforces 1140C — Playlist: a Go solution using stack-based processing. Learn the idea, check the complexity, and read the full code, with credit to EndlessCheng Codeforces Go.

Technique
Stack-based processing
Source
EndlessCheng Codeforces Go
Length
38 lines
Start with the idea.

Try the problem first. If you get stuck, read the approach below, then write your own solution. The full code is at the bottom.

Approach

Stack-based processing

For Codeforces 1140C — Playlist, the implementation keeps unresolved items in last-in, first-out order, often to match boundaries, parse structure, or maintain monotonic candidates.

  1. Define what every stack entry represents.
  2. Pop entries once the current item resolves or invalidates them.
  3. Push the current item with only the information later steps need.

Code notes

  • 38 lines of Go from the credited upstream file 1140C.go.
  • The implementation visibly relies on sequence storage.
  • No explicit loop blocks detected.

Complexity

If each item is pushed and popped at most once, the stack work is linear.

Check the problem constraints before deciding whether this complexity will pass.

Source

Code and credit

This code comes from EndlessCheng Codeforces Go by Σndless (EndlessCheng) and is used under the MIT licence.

Open problem ↗Original source ↗
Full codeCodeforces 1140C — Playlist · GoGo
Use this to learn the idea, then write your own version.
package main import (	"bufio"	"container/heap"	. "fmt"	"io"	"sort") // https://space.bilibili.com/206214func CF1140C(_r io.Reader, out io.Writer) {	in := bufio.NewReader(_r)	var n, k, ans, sum int	Fscan(in, &n, &k)	a := make([]struct{ len, b int }, n)	for i := range a {		Fscan(in, &a[i].len, &a[i].b)	}	sort.Slice(a, func(i, j int) bool { return a[i].b > a[j].b }) 	h := &hp40{}	for _, p := range a {		heap.Push(h, p.len)		sum += p.len		for h.Len() > k {			sum -= heap.Pop(h).(int)		}		ans = max(ans, sum*p.b)	}	Fprint(out, ans)} //func main() { CF1140C(os.Stdin, os.Stdout) }type hp40 struct{ sort.IntSlice }func (h *hp40) Push(v any) { h.IntSlice = append(h.IntSlice, v.(int)) }func (h *hp40) Pop() any   { a := h.IntSlice; v := a[len(a)-1]; h.IntSlice = a[:len(a)-1]; return v }

Keep practising

Did this explanation save you time? I'm a Grade 11 student building this free library to make difficult algorithms easier to understand.

Buy me a coffee ↗