can anyone give idea , how to solve question 4 in order of time complexity N , atcoder beginner contest 159. Link: https://atcoder.jp/contests/abc159/tasks/abc159_d
can anyone give idea , how to solve question 4 in order of time complexity N , atcoder beginner contest 159. Link: https://atcoder.jp/contests/abc159/tasks/abc159_d
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First take a map, iterate through array once and calculate number of balls for each number i.e.
m[a[i]]++;
Now iterate through map and calculate sum of number of ways of choosing 2 balls for each number
for(auto i:m) total_count+=((i.second)(i.second-1))/2
Now all you need to do is to go through the array one more time and print
total_count-m[a[i]]*(m[a[i]]-1)/2+(m[a[i]]-1)*(m[a[i]]-2)/2
for each element.Idea is to first subtract number of ways of choosing two balls from m[a[i]] balls and then add number of ways of choosing two balls from m[a[i]]-1 balls.
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