First and last appearance#4726

First and last appearance (Editorial)

Count the number of occurrences of the letter ' $f$ ' in the string, keeping track of the indices of its first and last appearances.

Algorithm implementation

Read the string character by character until the end (up to the ' $\n$ ' character). The index of the current character is stored in the variable $in d$ . The number of occurrences of the letter ' $f$ ' is counted in the variable $c n t$ .

cnt = 0; ind = 0;
while(scanf("%c",&ch), ch != '\n')
{

The variables $f$ and $s$ store the indices of the first and last appearances of the letter ' $f$ '.

  if (ch == 'f')
  {

If the letter ' $f$ ' is encountered and it appears for the first time (the variable $c n t$ is equal to $0$ ), the current index is assigned to the variable $f$ .

    if (cnt == 0) f = ind;

The letter ' $f$ ' is not encountered for the first time (if $c n t > 0$ cnt > 0). Assign the current index $in d$ to the variable $s$ .

    if (cnt > 0) s = ind;
    cnt++;
  }
  ind++;
}

Print the result based on the number of occurrences of the letter ' $f$ ' in the string.

if (cnt == 1)
  printf("%d\n",f);
else 
if (cnt > 1)
   printf("%d %d\n",f,s);

Java implementation

import java.util.*;

public class Main
{  
  public static void main(String[] args)
  {
    Scanner con = new Scanner(System.in);
    String str = con.nextLine(); 
    int first = str.indexOf("f");
    int last = str.lastIndexOf("f");
    if (first != -1)
    {
      if (first == last) System.out.println(first);
      else System.out.println(first + " " + last);
    }	
  }  
}

Java

Python implementation

Read the input string.

s = input()

Find the indices of the first and last occurrences of the symbol ' $f$ '.

first_index = s.find('f')
last_index = s.rfind('f')

Print the answer.

if first_index == -1:

The letter ' $f$ ' does not occur.

  pass
elif first_index == last_index:

The letter ' $f$ ' occurs only once.

  print(first_index)
else:

The letter ' $f$ ' occurs two or more times.

  print(first_index, last_index)