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Problem solution · Go

Codeforces 1107G — Vasya and Maximum Profit

Codeforces 1107G — Vasya and Maximum Profit: a Go solution using sliding window or two pointers. Learn the idea, check the complexity, and read the full code, with credit to EndlessCheng Codeforces Go.

Technique
Sliding window or two pointers
Source
EndlessCheng Codeforces Go
Length
78 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

Sliding window or two pointers

For Codeforces 1107G — Vasya and Maximum Profit, the implementation maintains a moving interval and updates only the information that enters or leaves the window.

  1. Choose the invariant that makes a window valid or useful.
  2. Advance the right boundary and add the new element.
  3. Move the left boundary only as needed while maintaining the invariant and updating the answer.

Code notes

  • 78 lines of Go from the credited upstream file 1107G.go.
  • The implementation visibly relies on sequence storage.
  • No explicit loop blocks detected.

Complexity

Confirm that neither pointer moves backwards; if so, the scan is usually linear apart from the window’s data-structure operations.

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 1107G — Vasya and Maximum Profit · GoGo
Use this to learn the idea, then write your own version.
package main import (	. "fmt"	"io"	"math/bits"	"slices") // https://github.com/EndlessChengtype st07 [][19][2]int func newST07(a []int) st07 {	n := len(a)	st := make(st07, n)	for i, v := range a {		st[i][0] = [2]int{v, v}	}	for j := 1; j < 19; j++ {		for i := range n - 1<<j + 1 {			st[i][j][0] = min(st[i][j-1][0], st[i+1<<(j-1)][j-1][0])			st[i][j][1] = max(st[i][j-1][1], st[i+1<<(j-1)][j-1][1])		}	}	return st} func (st st07) query(l, r int) [2]int {	k := bits.Len(uint(r-l)) - 1	p, q := st[l][k], st[r-1<<k][k]	return [2]int{min(p[0], q[0]), max(p[1], q[1])}} func cf1107G(in io.Reader, out io.Writer) {	var n, earn, c, ans int	Fscan(in, &n, &earn)	d := make([]int, n)	s := make([]int, n+1)	for i := range d {		Fscan(in, &d[i], &c)		s[i+1] = s[i] + earn - c		ans = max(ans, earn-c)	}	t := newST07(s) 	type pair struct{ d, i int }	ds := make([]pair, n-1)	left := make([]int, n-1)	st := []int{-1}	for i := range n - 1 {		v := d[i+1] - d[i]		ds[i] = pair{v, i}		for len(st) > 1 && d[st[len(st)-1]+1]-d[st[len(st)-1]] <= v {			st = st[:len(st)-1]		}		left[i] = st[len(st)-1]		st = append(st, i)	}	right := make([]int, n-1)	st = []int{n - 1}	for i := n - 2; i >= 0; i-- {		for len(st) > 1 && d[st[len(st)-1]+1]-d[st[len(st)-1]] <= d[i+1]-d[i] {			st = st[:len(st)-1]		}		right[i] = st[len(st)-1]		st = append(st, i)	} 	slices.SortFunc(ds, func(a, b pair) int { return a.d - b.d })	for _, p := range ds {		i := p.i		ans = max(ans, t.query(i+2, right[i]+2)[1]-t.query(left[i]+1, i+1)[0]-p.d*p.d)	}	Fprint(out, ans)} //func main() { cf1107G(bufio.NewReader(os.Stdin), os.Stdout) }

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