I'm quite new to JavaScript and I'm trying to implement my code in pseudocode in JavaScript, however I'm not getting the result that I'm supposed to. I want the function to permute the elements of the array p places to the left. In pseudocode I'm using a queue data structure, but I thought I can as well us an array. As the result of my function, I get an array with [2, 2, 2, 2]. Can you please help me out?
My code in pseudocode:
Function PERMUTEVECTOR(row, p)
If p=0 then
Return row
End if
New Queue q
For 0<= i <4 do
ENQUEUE[row[i], q]
End for
For 1<= i <= p do
ENQUEUE[HEAD[q],q]
DEQUEUE[q]
End for
For 0<=i<4 do
Row[i] <- HEAD[q]
DEQUEUE[q]
End for
Return row
End function
My code in JavaScript:
function permute_vector(row, p)
{
if (p=0)
{return row}
let q = new Array()
for (i=0; i<4; i )
{
q.push(row[i])
}
for (i=0; i<p; i )
{
q.push(q[0])
q.pop()
}
for (i=0; i<4; i )
{
row[i] = q[0]
q.pop()
}
return row
}
px = permute_vector([2,4,1,3], 1)
console.log("px is:", px)
}
I did the same in Python and it works fine:
def permute_vector(row, p):
if p==0:
return row
q = []
for i in range(4):
q.append(row[i])
for i in range(p):
q.append(q[0])
q.pop(0)
for i in range(4):
row[i] = q[0]
q.pop(0)
return row
What am I doing wrong with my JavaScript code?
Many thanks!
CodePudding user response：
if (p=0) {return row}
this should be if (p === 0) {return row}
CodePudding user response：
In javascript, Array.pop() removes the last element. You need Array.shift() for removing the first one.
function permute_vector(row, p)
{
if (p===0) // in js, checks are with == (loose) or === (strict).
// = is for assignment and you were assigning p to 0 here.
{return row}
let q = new Array()
for (i=0; i<4; i )
{
q.push(row[i])
}
for (i=0; i<p; i )
{
q.push(q[0])
q.shift() // shift instead of pop
}
for (i=0; i<4; i )
{
row[i] = q[0]
q.shift() // shift instead of pop
}
return row
}
px = permute_vector([2,4,1,3], 1)
console.log("px is:", px)
}
CodePudding user response：
Two mistakes:
- Comparisons need double or triple equal signs. In fact, you should prefer triple equal signs as you can read in this question/answer.
- In python
pop()accepts an index to remove a specific item. You're making use of that to remove the first item. In JavaScriptArray.pop()merely is capable of removing the last item. UseArray.shift()to remove the first item.
Working code:
function permute_vector(row, p) {
if (p === 0) {
return row;
}
let q = new Array();
for (i = 0; i < 4; i ) {
q.push(row[i]);
}
for (i = 0; i < p; i ) {
q.push(q[0]);
q.shift();
}
for (i = 0; i < 4; i ) {
row[i] = q[0];
q.shift();
}
return row;
}
px = permute_vector([2, 4, 1, 3], 1);
console.log("px is:", px);