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Problem solution · Go

Codeforces 296B — Yaroslav and Two Strings

Codeforces 296B — Yaroslav and Two Strings: a Go solution using direct simulation. Learn the idea, check the complexity, and read the full code, with credit to EndlessCheng Codeforces Go.

Technique
Direct simulation
Source
EndlessCheng Codeforces Go
Length
70 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

Direct simulation

For Codeforces 296B — Yaroslav and Two Strings, the implementation follows the problem’s operations directly while maintaining only the state needed for the next decision.

  1. Translate each rule into one explicit state update.
  2. Maintain the invariant after every processed item.
  3. Return the accumulated state once all relevant input has been handled.

Code notes

  • 70 lines of Go from the credited upstream file 296B.go.
  • The implementation keeps its working state in language-native values and containers.
  • No explicit loop blocks detected.

Complexity

Count the number and nesting of passes over the input, then include the maintained containers in the memory estimate.

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 296B — Yaroslav and Two Strings · GoGo
Use this to learn the idea, then write your own version.
package main import (	"bufio"	. "fmt"	"io") // https://space.bilibili.com/206214func cf296B(in io.Reader, out io.Writer) {	const mod = 1_000_000_007	var n int	var s, t string	var le, gr bool	Fscan(bufio.NewReader(in), &n, &s, &t)	all, same := 1, 1	for i := range s {		v, w := s[i], t[i]		if v == '?' || w == '?' {			if v == '?' {				all = all * 10 % mod			}			if w == '?' {				all = all * 10 % mod			}			if v == '?' && w == '?' {				same = same * 10 % mod			}		} else if v < w {			le = true		} else if v > w {			gr = true		}	}	if le && gr {		Fprint(out, all)		return	} 	res1, res2 := 1, 1	for i, v := range s {		w := t[i]		if v == '?' {			if w == '?' {				res1 = res1 * 55 % mod				res2 = res2 * 55 % mod			} else {				res1 = res1 * int(w-'0'+1) % mod				res2 = res2 * int('9'-w+1) % mod			}		} else if w == '?' {			res1 = res1 * int('9'-v+1) % mod			res2 = res2 * int(v-'0'+1) % mod		}	} 	if !gr {		all -= res1	}	if !le {		all -= res2	}	if !le && !gr {		all += same	}	Fprint(out, (all%mod+mod)%mod)} //func main() { cf296B(os.Stdin, os.Stdout) }

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