CP Week 1

 

Day 1 – Basics: Input, Output, If-Else, Loops

📘 Focus Topic: Syntax, loops, if-else

1. 71A – Way Too Long Words

#include <stdio.h>

#include <string.h>

int main() {

    int n;

    scanf("%d", &n);  // Read number of test cases

    for (int i = 0; i < n; i++) {

        char str[101];  // Word length can be up to 100 + 1 for null terminator

        scanf("%s", str);

        int len = strlen(str);

        if (len > 10) {

            printf("%c%d%c\n", str[0], len - 2, str[len - 1]);

        } else {

            printf("%s\n", str);

        }

    }

    return 0;

}

Here i havenot used getchar or fgets, the create confusion in cf. then, [101] cause

there is also null '\0' that is space, scanf will not scan space, but it will consume

a storage, so 101 is a must.. it will not affect other code.

if length>10 is a guess, so try hard to guess!

1. 4A – Watermelon

easy

1. 231A – Team

easy

1. 1A – Theatre Square

here we should use long long, long double (%Lf) often. Int a/ int b= int value; if we want a float then (float)a/ b; it should be. Remember;

1. 112A – Petya and Strings

2. 282A – Bit++

3. 50A – Domino Piling

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✅ Day 2 – Basic Math & Brute Force

📘 Focus Topic: Modulo, math, loops

1. 617A – Elephant

2. 158A – Next Round

3. 546A – Soldier and Bananas

4. 734A – Anton and Danik

5. 791A – Bear and Big Brother

6. 1328A – Divisibility Problem

7. 1353B – Two Arrays And Swaps

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✅ Day 3 – Arrays: Traversal & Counting

📘 Focus Topic: Array operations, min/max

1. 318A – Even Odds

2. 69A – Young Physicist

3. 734B – Anton and Digits

4. 236A – Boy or Girl

5. 339A – Helpful Maths

6. 59A – Word

7. 110A – Nearly Lucky Number

Completed!

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✅ Day 4 – Strings: Manipulation & Counting

📘 Focus Topic: Strings, case conversion, frequency

1. 281A – Word Capitalization

2. 41A – Translation

3. 116A – Tram

4. 785A – Anton and Polyhedrons

5. 977A – Wrong Subtraction

6. 1335A – Candies and Two Sisters

7. 263A – Beautiful Matrix

Completed

Task	How to solve
Is string a palindrome?	Compare front and back chars using 2-pointer
Anagram check?	Compare character frequency arrays
Count vowels/digits/specials	`if (ch == 'a'
Case-insensitive comparison	Convert both strings to same case first
Remove duplicates	Use boolean array or frequency array

Concepts:

1.  frequency count in string:

int freq[26] = {0};  // for 'a' to 'z'

for (int i = 0; str[i]; i++) {

    if (str[i] >= 'a' && str[i] <= 'z') {

        freq[str[i] - 'a']++;

    }

}

angram check:

#include<stdio.h>

#include<string.h>

#include<stdlib.h>

int asc(const void *a, const void *b)

{  return(*(int*)a-*(int*)b);

}

int main()

{ //silent listen

    char str1[8]="teacher";

    char str2[8]="cheater";

    int ascii1[100]; int k=0;

    for(int i=0; str1[i]!='\0';i++)

    {

        ascii1[k++]=(int)str1[i];

    }

   

 int ascii2[100]; int l=0;

    for(int i=0; str2[i]!='\0';i++)

    {

        ascii2[l++]=(int)str2[i];

    }

   

qsort(ascii1, k, sizeof(int), asc);

qsort(ascii2, l, sizeof(int), asc);

for(int i=0; i<k; i++)

{

    str1[i]=(char)ascii1[i];

}

for(int i=0; i<l; i++)

{

    str2[i]=(char)ascii2[i];

}

int result= strcmp(str1, str2);

printf("%d", result);

}

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✅ Day 5 – Sorting & Greedy Basics

🔍 Core Basics of Sorting Problems

1. ✅ Sort Numbers

Concept: Just sort numbers in ascending or descending order.

Skills: Use built-in sorting (qsort() in C) or manually sort.

📌 Example:

Input: 3 1 2 → Output: 1 2 3

🧪 Practice:

• CF 339A – Helpful Maths

• CF 474A – Keyboard

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2. 🧠 Sort Strings

Concept: Sort strings alphabetically or by length.

📌 Example:

Input: bat, apple, car → After sort: apple bat car

🧪 Practice:

• CF 118A – String Task

• CF 58A – Chat room

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3. 📦 Sort with Original Index

Concept: Keep track of original position after sorting.

Technique: Use a struct or two arrays — one for value, one for original index.

🧪 Practice:

• CF 405A – Gravity Flip

• CF 263A – Beautiful Matrix

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4. 🎯 Sort Then Greedy Selection

Concept: After sorting, make the best decision step-by-step.

📌 Example:

Pick smallest tasks first, or minimize cost.

🧪 Practice:

• CF 160A – Twins

• CF 999B – Reversing Encryption

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5. 📊 Sort + Frequency

Concept: Sort array and count how many times each number appears.

📌 Example:

Check if any number occurs more than once after sorting.

🧪 Practice:

• CF 4A – Watermelon

• CF 228A – Is your horseshoe on the other hoof?

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6. 🔁 Two Pointers after Sort

Concept: After sorting, use two pointers from left and right to pair elements.

🧪 Practice:

• CF 327A – Flipping Game

• CF 550A – Two Substrings

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✅ Daily Practice Plan (Beginner Sorting)

Try to solve 2 problems/day for the next few days:

Day 1:

• CF 339A – Helpful Maths

• CF 160A – Twins

Day 2:

• CF 405A – Gravity Flip

• CF 228A – Horseshoe

Day 3:

• CF 118A – String Task

• CF 977B – Two-gram

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📘 Focus Topic: Sorting for simplification

1. 758A – Holiday Of Equality

2. 144A – Arrival of the General

3. 339B – Xenia and Ringroad

4. 977B – Two-gram

5. 266A – Stones on the Table

6. [281A – Word Capitalization](repeat for review)

7. [112A – Petya and Strings](repeat for mastery)

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✅ Day 6 – Review + Missed Problems

📘 Focus: Re-solve or finish any from earlier days

• Pick 4 problems you failed or skipped.

• Solve 3 new problems in your comfort range:

  • [339A – Helpful Maths](again for sorting)

  • [546A – Soldier and Bananas](easy math)

  • [1A – Theatre Square](geometry basics)

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✅ Day 7 – Simulated Contest Day

📘 Focus: Build contest skill under pressure

Solve these 7 problems in one sitting (90–120 mins):

1. 71A – Way Too Long Words

2. [158A – Next Round](math + condition)

3. 231A – Team

4. [282A – Bit++](easy loop)

5. [69A – Young Physicist](array + logic)

6. 339A – Helpful Maths

7. [236A – Boy or Girl](string frequency)

LAST TASK:

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 Gellyfish and Baby's Breath