 CHEFSIGN - Editorial

#1

Author: Dmytro Berezin
Primary Tester: Misha Chorniy
Editorialist: Hussain Kara Fallah

Cakewalk

None

PROBLEM:

Given a sequence of N arithmetic signs ( = , + , - ) between N+1 unknown integers. You are allowed to fix these integers using numbers in the range [1,P] such that the expression is true when you read it from left to right. (Numbers don’t violate the signs). You are asked to calculate minimum possible P such you can construct a valid expression.

EXPLANATION:

First of all, it’s clear that we can drop all ‘=’ signs and pretend that they never existed, because each number which follows an ‘=’ sign would be identical to the number preceding this sign. So these signs aren’t affecting our answer at all.

P = max(maximum number of consecutive ‘<’ signs, maximum number of consecutive ‘>’ signs) + 1

Let’s process our expression from left to right, If we are facing X (X ≤ P-1) consecutive ‘<’ signs, our starting number would be P-X, and we increment our last number by 1 after each sign,so the number after the last sign would be exactly P (which will be followed by ‘>’ sign). Our last number will be followed by Y consecutive ‘>’ signs, so we assign the next number to Y (Y < P) and we decrement the last number by 1 by each ‘>’ sign we process. The number after the last sign would be 1. (In case our expression starts with ‘>’ the situation would just be reversed).
After that we would have another block of Z consecutive ‘<’ signs, so we assign the next number to P-Z (P-Z ≥ 1) so the number after the last sign would be P and we continue…

Following this approach, the last number after a block of consecutive ‘<’ signs would be P (the maximal value), and the last number after a block of consecutive ‘>’ signs would be 1 (the minimal value). So according to our bold assumption below we can assign values using numbers in the range [1,P] without violating the signs.

Let’s take an example:

<<<=>=>=>>><<>>>><<<<<>><<>>

After removing = signs our sequence would be

<<< >>>>> << >>>> << >>>>>

(Blocks are separated by spaces for clarity)

here P = max(3 , 5 , 2 , 4 , 5 , 2 , 2 , 2) + 1 = 6

Our sequence would be

3 < 4 < 5 < 6 > 5 > 4 > 3 > 2 > 1 < 5 < 6 > 4 > 3 > 2 > 1 < 5 < 6 > 5 > 4 > 3 > 2 > 1

AUTHOR’S AND TESTER’S SOLUTIONS:

TESTER’s solution: Will be found here
EDITORIALIST’s solution: Will be found here

#2

could any one tell why this gives WA https://www.codechef.com/viewsolution/14569995

#3

I am also getting few of the testcases accepted and others wrong answer.
https://www.codechef.com/viewsolution/14563406

``````#include <iostream>
#define lli long long int
using namespace std;

int main(void) {
int t;
cin >> t;
while(t--){
char s;
lli tmp = 1, pmax = 1, pmin = 1;
lli i;
lli ans;
cin >> s;
for(i = 0; s* != '\0'; i++){
if(s* == '<'){
tmp++;
} else if(s* == '>'){
tmp--;
}
if(pmax < tmp) pmax = tmp;
if(pmin > tmp) pmin = tmp;
}
//cout << pmax << " " << pmin << endl;
if(pmin < 1) {
ans = pmax - pmin + 1;
} else {
ans = pmax;
}
cout << ans << endl;
}
return 0;
}``````

#4

Yes, In both of your codes, you guys are assuming that the numbers increase or decrease by 1, which is not always the case.
Consider this,
str = ‘><<<><<’

but the actual answer would be 4
== 2>1<2<3<4>1<2<3

like this.

#5

Here is my code … what do you think is wrong about it. Please, help me find my mistakes

``````#include <bits/stdc++.h>

using namespace std;

#define fast_cin ios_base::sync_with_stdio(false)

typedef long long ll;

int main()
{
fast_cin;
ll t; cin >> t;
while(t--){
string s; cin >> s;
ll in = 1, ans = 0;
for (int i = 0; i < s.size(); ++i)
{
if (s* == '<')
{
in++;
ans = max(ans,in);
}
else if (s* == '>')
{
in = 1;
}
}
cout << ans << endl;
}

return 0;
}
``````

It is giving current answer for string s = '<<<=>=>=>>><<>>>><<<<<>><<>>'or ‘><<<><<’

#6

can any one pls tell me why am i not able to pass 2 cases in main task… ? i have my code and screen shot of my result here…

https://pastebin.com/6QJRau0v

#7

Can anybody tell me what’s wrong with it.

https://www.codechef.com/viewsolution/14523196