Tasks Details
medium
1.
Flags
Find the maximum number of flags that can be set on mountain peaks.
Task Score
53%
Correctness
75%
Performance
28%
A non-empty array A consisting of N integers is given.
A peak is an array element which is larger than its neighbours. More precisely, it is an index P such that 0 < P < N − 1 and A[P − 1] < A[P] > A[P + 1].
For example, the following array A:
A[0] = 1 A[1] = 5 A[2] = 3 A[3] = 4 A[4] = 3 A[5] = 4 A[6] = 1 A[7] = 2 A[8] = 3 A[9] = 4 A[10] = 6 A[11] = 2has exactly four peaks: elements 1, 3, 5 and 10.
You are going on a trip to a range of mountains whose relative heights are represented by array A, as shown in a figure below. You have to choose how many flags you should take with you. The goal is to set the maximum number of flags on the peaks, according to certain rules.
Flags can only be set on peaks. What's more, if you take K flags, then the distance between any two flags should be greater than or equal to K. The distance between indices P and Q is the absolute value |P − Q|.
For example, given the mountain range represented by array A, above, with N = 12, if you take:
- two flags, you can set them on peaks 1 and 5;
- three flags, you can set them on peaks 1, 5 and 10;
- four flags, you can set only three flags, on peaks 1, 5 and 10.
You can therefore set a maximum of three flags in this case.
Write a function:
int solution(vector<int> &A);
that, given a non-empty array A of N integers, returns the maximum number of flags that can be set on the peaks of the array.
For example, the following array A:
A[0] = 1 A[1] = 5 A[2] = 3 A[3] = 4 A[4] = 3 A[5] = 4 A[6] = 1 A[7] = 2 A[8] = 3 A[9] = 4 A[10] = 6 A[11] = 2the function should return 3, as explained above.
Write an efficient algorithm for the following assumptions:
- N is an integer within the range [1..400,000];
- each element of array A is an integer within the range [0..1,000,000,000].
Copyright 2009–2024 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.
Solution
Programming language used C++
Time spent on task 6 minutes
Notes
not defined yet
Task timeline
Code: 15:09:08 UTC,
java,
autosave
Code: 15:09:35 UTC,
java,
autosave
// you can use includes, for example:
// #include <algorithm>
#include <cstdlib>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
int solution(vector<int> &A) {
// write your code in C++14 (g++ 6.2.0)
vector<int> v;
int count = 1, cmp = 0;
if(A[0] > A[1])
v.emplace_back(0);
for(int i = 1; i < A.size() - 1; i++){
if(A[i - 1] < A[i] && A[i] > A[i + 1])
v.emplace_back(i);
}
if(A[A.size() - 1] > A[A.size() - 2])
v.emplace_back(A.size() - 1);
if(v.size() == 0) return 0;
if(v.size() == 1) return 1;
int flag = 2;
while(true){
int num = v[0];
for(int i = 1; i < v.size(); i++){
if(abs(num - v[i]) > flag){
count++;
num = v[i];
if(flag == count){
cmp = count;
count = 1;
break;
}
}
}
if(flag > cmp)
return cmp;
flag++;
}
}
Code: 15:09:35 UTC,
cpp,
autosave
Code: 15:09:40 UTC,
cpp,
autosave
// you can use includes, for example:
// #include <algorithm>
#include <cstdlib>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
int solution(vector<int> &A) {
// write your code in C++14 (g++ 6.2.0)
vector<int> v;
int count = 1, cmp = 0;
if(A[0] > A[1])
v.emplace_back(0);
for(int i = 1; i < A.size() - 1; i++){
if(A[i - 1] < A[i] && A[i] > A[i + 1])
v.emplace_back(i);
}
if(A[A.size() - 1] > A[A.size() - 2])
v.emplace_back(A.size() - 1);
if(v.size() == 0) return 0;
if(v.size() == 1) return 1;
int flag = 2;
while(true){
int num = v[0];
for(int i = 1; i < v.size(); i++){
if(abs(num - v[i]) > flag){
count++;
num = v[i];
if(flag == count){
cmp = count;
count = 1;
break;
}
}
}
if(flag > cmp)
return cmp;
flag++;
}
}
Code: 15:10:00 UTC,
cpp,
autosave
// you can use includes, for example:
// #include <algorithm>
#include <cstdlib>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
int solution(vector<int> &A) {
// write your code in C++14 (g++ 6.2.0)
vector<int> v;
int count = 1, cmp = 0;
for(int i = 1; i < A.size() - 1; i++){
if(A[i - 1] < A[i] && A[i] > A[i + 1])
v.emplace_back(i);
}
if(A[A.size() - 1] > A[A.size() - 2])
v.emplace_back(A.size() - 1);
if(v.size() < 2) return v.size();
int flag = 2;
while(true){
int num = v[0];
for(int i = 1; i < v.size(); i++){
if(abs(num - v[i]) > flag){
count++;
num = v[i];
if(flag == count){
cmp = count;
count = 1;
break;
}
}
}
if(flag > cmp)
return cmp;
flag++;
}
}
Code: 15:10:21 UTC,
cpp,
autosave
// you can use includes, for example:
// #include <algorithm>
#include <cstdlib>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
int solution(vector<int> &A) {
// write your code in C++14 (g++ 6.2.0)
vector<int> v;
int count = 1, cmp = 0;
for(int i = 1; i < A.size() - 1; i++){
if(A[i - 1] < A[i] && A[i] > A[i + 1])
v.emplace_back(i);
}
if(v.size() < 2) return v.size();
if(A[A.size() - 1] > A[A.size() - 2])
v.emplace_back(A.size() - 1);
int flag = 2;
while(true){
int num = v[0];
for(int i = 1; i < v.size(); i++){
if(abs(num - v[i]) > flag){
count++;
num = v[i];
if(flag == count){
cmp = count;
count = 1;
break;
}
}
}
if(flag > cmp)
return cmp;
flag++;
}
}
Code: 15:10:41 UTC,
cpp,
autosave
// you can use includes, for example:
// #include <algorithm>
#include <cstdlib>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
int solution(vector<int> &A) {
// write your code in C++14 (g++ 6.2.0)
vector<int> v;
int count = 1, cmp = 0;
for(int i = 1; i < A.size() - 1; i++){
if(A[i - 1] < A[i] && A[i] > A[i + 1])
v.emplace_back(i);
}
if(v.size() < 2) return v.size();
if(A[A.size() - 1] > A[A.size() - 2]){
v.pop_back();
v.emplace_back(A.size() - 1);
}
int flag = 2;
while(true){
int num = v[0];
for(int i = 1; i < v.size(); i++){
if(abs(num - v[i]) > flag){
count++;
num = v[i];
if(flag == count){
cmp = count;
count = 1;
break;
}
}
}
if(flag > cmp)
return cmp;
flag++;
}
}
Code: 15:10:51 UTC,
cpp,
autosave
// you can use includes, for example:
// #include <algorithm>
#include <cstdlib>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
int solution(vector<int> &A) {
// write your code in C++14 (g++ 6.2.0)
vector<int> v;
int count = 1, cmp = 0;
for(int i = 1; i < A.size() - 1; i++){
if(A[i - 1] < A[i] && A[i] > A[i + 1])
v.emplace_back(i);
}
if(v.size() < 2) return v.size();
if(A[A.size() - 1] > A[A.size() - 2]){
v.pop_back();
v.emplace_back(A.size() - 1);
}
int flag = 2;
while(true){
int num = v[0];
for(int i = 1; i < v.size(); i++){
if(abs(num - v[i]) > flag){
count++;
num = v[i];
if(flag == count){
cmp = count;
count = 1;
break;
}
}
}
if(flag > cmp)
return cmp;
flag++;
}
}
Code: 15:11:07 UTC,
cpp,
autosave
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
int solution(vector<int> &A) {
// write your code in C++14 (g++ 6.2.0)
vector<int> v;
int count = 1, cmp = 0;
for(int i = 1; i < A.size() - 1; i++){
if(A[i - 1] < A[i] && A[i] > A[i + 1])
v.emplace_back(i);
}
if(v.size() < 2) return v.size();
if(A[A.size() - 1] > A[A.size() - 2]){
v.pop_back();
v.emplace_back(A.size() - 1);
}
int flag = 2;
while(true){
int num = v[0];
for(int i = 1; i < v.size(); i++){
if(v[i] - num > flag){
count++;
num = v[i];
if(flag == count){
cmp = count;
count = 1;
break;
}
}
}
if(flag > cmp)
return cmp;
flag++;
}
}
Code: 15:11:28 UTC,
cpp,
verify,
result: Passed
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
int solution(vector<int> &A) {
// write your code in C++14 (g++ 6.2.0)
vector<int> v;
int count = 1, cmp = 0;
for(int i = 1; i < A.size() - 1; i++){
if(A[i - 1] < A[i] && A[i] > A[i + 1])
v.emplace_back(i);
}
if(v.size() < 2) return v.size();
if(A[A.size() - 1] > A[A.size() - 2]){
v.pop_back();
v.emplace_back(A.size() - 1);
}
int flag = 2;
while(true){
int num = v[0];
for(int i = 1; i < v.size(); i++){
if(v[i] - num > flag){
count++;
num = v[i];
if(flag == count){
cmp = count;
count = 1;
break;
}
}
}
if(flag > cmp)
return cmp;
flag++;
}
}
Analysis
Code: 15:14:18 UTC,
cpp,
verify,
result: Passed
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
int solution(vector<int> &A) {
// write your code in C++14 (g++ 6.2.0)
vector<int> v;
int count = 1, cmp = 0;
for(int i = 1; i < A.size() - 1; i++){
if(A[i - 1] < A[i] && A[i] > A[i + 1])
v.emplace_back(i);
}
if(v.size() < 2) return v.size();
if(A[A.size() - 1] > A[A.size() - 2]){
v.pop_back();
v.emplace_back(A.size() - 1);
}
int flag = 2;
while(true){
int num = v[0];
for(int i = 1; i < v.size(); i++){
if(v[i] - num > flag){
count++;
num = v[i];
if(flag == count){
cmp = count;
count = 1;
break;
}
}
}
if(flag > cmp)
return cmp;
flag++;
}
}
Analysis
Code: 15:14:21 UTC,
cpp,
final,
score:
53
// you can use includes, for example:
// #include <algorithm>
// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;
int solution(vector<int> &A) {
// write your code in C++14 (g++ 6.2.0)
vector<int> v;
int count = 1, cmp = 0;
for(int i = 1; i < A.size() - 1; i++){
if(A[i - 1] < A[i] && A[i] > A[i + 1])
v.emplace_back(i);
}
if(v.size() < 2) return v.size();
if(A[A.size() - 1] > A[A.size() - 2]){
v.pop_back();
v.emplace_back(A.size() - 1);
}
int flag = 2;
while(true){
int num = v[0];
for(int i = 1; i < v.size(); i++){
if(v[i] - num > flag){
count++;
num = v[i];
if(flag == count){
cmp = count;
count = 1;
break;
}
}
}
if(flag > cmp)
return cmp;
flag++;
}
}Analysis summary
The following issues have been detected: wrong answers.
Analysis
expand all
Correctness tests
1.
0.001 s
OK
2.
0.001 s
OK
3.
0.001 s
OK
1.
0.001 s
OK
2.
0.001 s
OK
3.
0.001 s
OK
4.
0.001 s
OK
5.
0.001 s
OK
1.
0.001 s
OK
2.
0.001 s
OK
1.
0.001 s
OK
1.
0.001 s
OK
1.
0.001 s
WRONG ANSWER,
got 27 expected 28
1.
0.001 s
OK
2.
0.001 s
OK
1.
0.001 s
WRONG ANSWER,
got 3 expected 4
2.
0.001 s
WRONG ANSWER,
got 98 expected 99
expand all
Performance tests
1.
0.016 s
WRONG ANSWER,
got 315 expected 316
2.
0.004 s
OK
1.
0.008 s
OK
2.
0.032 s
OK
1.
0.012 s
WRONG ANSWER,
got 312 expected 313
2.
0.012 s
OK
1.
0.020 s
OK
2.
0.008 s
WRONG ANSWER,
got 315 expected 316
1.
0.004 s
OK
2.
0.004 s
OK
1.
0.016 s
WRONG ANSWER,
got 598 expected 597
2.
0.008 s
OK
1.
0.032 s
WRONG ANSWER,
got 29 expected 30
2.
0.032 s
WRONG ANSWER,
got 29 expected 30