Compare each Pair of Elements in Array Without Repetition

Computer Science Level 1

We want to go over each pair of elements in array A A once. 

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for (let i = 0; i < A.length - 1; i++) {
  // inner loop
  ...
}

What is the correct expression for the inner loop?

for (j = i + 1; j < arr.length; j++) for (j = i; j < arr.length; j++) for (j = 0; j < arr.length; j++) for (j = i; j <= arr.length; j++)

フランスワ 砂取 by フランスワ 砂取 , 31, Canada

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2 solutions

I have objections to all of the answers. The first objection that it should not be arr; but, A. The second objection is that it should be ++j and not j++. Yes, modern compilers optimize away the unnecessary save of the original value of j. Yes, the example of a for loop on page 57 of the first edition of The C Programming Language by K&R shows a preincrement. As Dr. Kernighan worked short distance away from me at Bell Labs, I asked him about the use of a preincrement in this case and he said it was a mistake not caught in proofreading.

5 Helpful 2 Interesting 0 Brilliant 0 Confused
Keshav Garg
Dec 2, 2018

for (let i = 0; i < A.length - 1; i++) {

#means we are starting with A[0] upto A[A.lenght-1]

for(j=i+1;j< arr.length;j++){

#means we are starting the inner loop with A[i+1] upto A[A.lenght] ,whatever i is in the main loop ,our j will be one more than that

#which means the element with index i will have a pair with element with index i+1 which truly meets the required condition of not having the same pair twice

# 0,1 0,2 0,3 0,4 ....

#1,2 1,3 1,4.......

0 Helpful 0 Interesting 0 Brilliant 0 Confused

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