A non-empty array A consisting of N integers is given. The consecutive elements of array A represent consecutive cars on a road.
Array A contains only 0s and/or 1s:
- 0 represents a car traveling east,
- 1 represents a car traveling west.
The goal is to count passing cars. We say that a pair of cars (P, Q), where 0 ≤ P < Q < N, is passing when P is traveling to the east and Q is traveling to the west.
For example, consider array A such that:
A[0] = 0 A[1] = 1 A[2] = 0 A[3] = 1 A[4] = 1We have five pairs of passing cars: (0, 1), (0, 3), (0, 4), (2, 3), (2, 4).
Write a function:
function solution(A);
that, given a non-empty array A of N integers, returns the number of pairs of passing cars.
The function should return −1 if the number of pairs of passing cars exceeds 1,000,000,000.
For example, given:
A[0] = 0 A[1] = 1 A[2] = 0 A[3] = 1 A[4] = 1the function should return 5, as explained above.
Write an efficient algorithm for the following assumptions:
- N is an integer within the range [1..100,000];
- each element of array A is an integer that can have one of the following values: 0, 1.
// 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)
}function solution(A) {
const AL = A.length;
const EAST = [];
const WEST = [];
let COUNT = 0;
for (I = 0; I < AL; I++) {
if (A[I] === 0) EAST.push(I);
else WEST.push(I);
}
const EL = EAST.length;
for (I = 0; I < EL; I++) {
let WI = WEST.indexOf(EAST[I] + 1);
COUNT += (WEST.length-WI);
}
return COUNT;
}
// 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)
}function solution(A) {
const AL = A.length;
const EAST = [];
const WEST = [];
let COUNT = 0;
for (I = 0; I < AL; I++) {
if (A[I] === 0) EAST.push(I);
else WEST.push(I);
}
const EL = EAST.length;
for (I = 0; I < EL; I++) {
let WI = WEST.indexOf(EAST[I] + 1);
COUNT += (WEST.length-WI);
}
return COUNT;
}
// 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)
}function solution(A) {
const AL = A.length;
const EAST = [];
const WEST = [];
let COUNT = 0;
for (I = 0; I < AL; I++) {
if (A[I] === 0) EAST.push(I);
else WEST.push(I);
}
const EL = EAST.length;
for (I = 0; I < EL; I++) {
let WI = WEST.indexOf(EAST[I] + 1);
COUNT += (WEST.length-WI);
}
return COUNT;
}
// 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)
}function solution(A) {
const AL = A.length;
const EAST = [];
const WEST = [];
let COUNT = 0;
for (I = 0; I < AL; I++) {
if (A[I] === 0) EAST.push(I);
else WEST.push(I);
}
const EL = EAST.length;
for (I = 0; I < EL; I++) {
let WI = WEST.indexOf(EAST[I] + 1);
COUNT += (WEST.length-WI);
}
return COUNT;
}
The following issues have been detected: wrong answers, timeout errors.
For example, for the input [0] the solution returned a wrong answer (got 1 expected 0).
random, length = ~100,000
running time: 3.96 sec., time limit: 0.38 sec.
0..01..1, length = ~100,000
running time: 5.28 sec., time limit: 0.38 sec.
0101..01, length = ~100,000
running time: 2.72 sec., time limit: 0.38 sec.