Asufe juniors-training session2

ASUFE Juniors
Training
Session II

Welcome to The Second Session of ASUFE Juniors
Training
• Session Agenda:
• Note about sharing problem code
• Revision on functions
• Complexity Analysis
• Problem types
• Thinking techniques
• Stack vs Heap
• Local variables vs Global variables

Note about sharing sheet
problems codes
• Do not share a code that got an accepted to the facebook group.
Why?

Revision on functions
• IDE examples

Time Complexity (Big O notation)

Time Complexity (Example 1)
Total runtime: O(n) - Constants are neglected

for (size_t i = 0; i < n; i++) {
/* code */
}
for (size_t i = 0; i < n; i++) {
for (size_t j = 0; j < m; j++) {
/* code */
}
}
for (size_t i = 1; i < n; i *= 2) {
for (size_t j = 0; i < n; j++) {
/* code */
}
}

for (size_t i = 0; i < n; i++) {
for (size_t j = i; j < n; j++) {
/* code */
}
}
≈ n + (n-1) + (n-2) + ... + 2 + 1
≈ n(n+1) / 2
≈ (n^2 + n) / 2 ≈ O(n^2)

Task: Search for an element in a sorted array.

Task: Search for an element in a sorted array.
Runtime Analysis:
Linear Search: O(n)
Binary Search: O(log n)
Space Analysis (Neglecting the original array):
Linear Search: O(1)
Binary Search: O(1)

Time Complexity
Most online judges run between 10^7 ~ 10^8 operation/second

Problem Types
• Brute force
• Greedy
• Ad hocs
• Divide and conquer

Problem statement
• Read the problem statement
• Think in a solution and verify it.
• Coding
• Debugging
• Testing

Problem statement
• Make sure you read the problem statement correctly.
• Reading the problem in hurry may lead that you solve another problem.
• Make sure to output the output format exactly as the problem asks.
• How codeforces and UVA judges handle new lines at the end of the output.
• Make sure to output the precision of the output as the problem asks.
• Make sure to check the problem constraints carefully.
• Don’t assume something not mentioned.
• Sometimes samples are trivial to mislead you.
• Think in papers not on pc.

Stack vs Heap
• Local variables go in the stack.
• Global variables go in the data section.
• Dynamically allocated variables go in the heap.
• Declare your variables locally vs declaring them globally.

ACM ICPC Rules
• More problems higher rank.
• If 2 contestants have the same number of problems then we see who
have a lower penalty time.
• Each problem penalty is added whenever we submit it accepted.
• Every wrong answer adds 20 mins penalty time.

Codeforces problems difficulty
• Div3 problems are the easiest.
• Div2 is harder.
• Div1 is the hardest.
• Each Div is composed of problems distributed from A to E or F
according to the contest.
• A is the easiest.
• As we go up in alphabet the problem becomes harder.
• ICPC problem distribution are different from codeforces.

Asufe juniors-training session2

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