Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Welcome To Ask or Share your Answers For Others

Categories

0 votes
809 views
in Technique[技术] by (71.8m points)

c++ - Number of swaps in Bubble Sort

I have a version of bubble sort:

int i, j;  

for i from n downto 1 
{
    for j from 1 to i-1 
    { 
        if (A[j] > A[j+1])
            swap(A[j], A[j+1]) 
    } 
}

I want to calculate the expected number of swaps using the above version of bubble sort. The method used by me is shown below :

// 0 based index

float ans = 0.0;

for ( int i = 0; i < n-1; i++ )
{
    for ( int j = i+1; j < n; j++ ) {

        ans += getprob( a[i], a[j]); // computes probability that a[i]>a[j].
    }
}

Am i going the correct way or am I missing something?

See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome To Ask or Share your Answers For Others

1 Reply

0 votes
by (71.8m points)

The best way to get the answer is by running the bubble-sort algorithm itself and including a counter after the swap() call. Your calculation function would (a) need almost as long as the sort itself (depending on the runtime of swap() vs. getprob()) and (b) miss the point that the order of the elements changes while sorting.

Btw, the exact number of swap() calls depends on the data you need to sort - you have n*(n-1)/2 comparisions and any of them could result in a swap (on average, half of the time you need to swap the compared elements).


与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
OGeek|极客中国-欢迎来到极客的世界,一个免费开放的程序员编程交流平台!开放,进步,分享!让技术改变生活,让极客改变未来! Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Click Here to Ask a Question

1.4m articles

1.4m replys

5 comments

56.8k users

...