Tasks Details
easy
Find the missing element in a given permutation.
Task Score
100%
Correctness
100%
Performance
100%
An array A consisting of N different integers is given. The array contains integers in the range [1..(N + 1)], which means that exactly one element is missing.
Your goal is to find that missing element.
Write a function:
function solution(A);
that, given an array A, returns the value of the missing element.
For example, given array A such that:
A[0] = 2 A[1] = 3 A[2] = 1 A[3] = 5the function should return 4, as it is the missing element.
Write an efficient algorithm for the following assumptions:
- N is an integer within the range [0..100,000];
- the elements of A are all distinct;
- each element of array A is an integer within the range [1..(N + 1)].
Copyright 2009–2025 by Codility Limited. All Rights Reserved. Unauthorized copying, publication or disclosure prohibited.
Solution
Programming language used JavaScript
Time spent on task 4 minutes
Notes
not defined yet
Code: 21:25:08 UTC,
java,
autosave
Code: 21:25:19 UTC,
js,
verify,
result: Passed
// you can write to stdout for debugging purposes, e.g.
// console.log('this is a debug message');
function solution(A) {
// write your code in JavaScript (Node.js 8.9.4)
const len = A.length;
let total = ((len + 2) * (len + 1)) / 2;
for (const a of A) {
total -= a;
}
return total;
}
Analysis
Code: 21:26:27 UTC,
js,
verify,
result: Passed
// you can write to stdout for debugging purposes, e.g.
// console.log('this is a debug message');
function solution(A) {
// write your code in JavaScript (Node.js 8.9.4)
const len = A.length;
let total = ((len + 2) * (len + 1)) / 2;
for (const a of A) {
total -= a;
}
return total;
}
User test case 1:
[2]
Analysis
Code: 21:26:43 UTC,
js,
verify,
result: Passed
// you can write to stdout for debugging purposes, e.g.
// console.log('this is a debug message');
function solution(A) {
// write your code in JavaScript (Node.js 8.9.4)
const len = A.length;
let total = ((len + 2) * (len + 1)) / 2;
for (const a of A) {
total -= a;
}
return total;
}
User test case 1:
[1]
Analysis
Code: 21:28:41 UTC,
js,
verify,
result: Passed
// you can write to stdout for debugging purposes, e.g.
// console.log('this is a debug message');
function solution(A) {
// write your code in JavaScript (Node.js 8.9.4)
const len = A.length;
let total = ((len + 2) * (len + 1)) / 2;
for (const a of A) {
total -= a;
}
return total;
}
User test case 1:
[1]
Analysis
Code: 21:28:43 UTC,
js,
final,
score:
100
// you can write to stdout for debugging purposes, e.g.
// console.log('this is a debug message');
function solution(A) {
// write your code in JavaScript (Node.js 8.9.4)
const len = A.length;
let total = ((len + 2) * (len + 1)) / 2;
for (const a of A) {
total -= a;
}
return total;
}
Analysis summary
The solution obtained perfect score.
Analysis
Detected time complexity:
O(N) or O(N * log(N))
expand all
Correctness tests
1.
0.068 s
OK
2.
0.068 s
OK
1.
0.068 s
OK
2.
0.068 s
OK
1.
0.072 s
OK
2.
0.068 s
OK
1.
0.068 s
OK
2.
0.068 s
OK
3.
0.072 s
OK
1.
0.072 s
OK
expand all
Performance tests
1.
0.080 s
OK
1.
0.080 s
OK
1.
0.116 s
OK
2.
0.104 s
OK
3.
0.100 s
OK
1.
0.112 s
OK
1.
0.104 s
OK