Setter-pavan sai kiran
Editorialpavan sai kiran
sequence and series,floyd triangle
According to the problem,you just have to find the string ‘B’ from the given string ‘A’ and find the kth character in the string ‘B’.
let us take String ‘A’ as “abcd” and k be 15, so now the string ‘B’ will be
a a b a b c a b c d b b c b c d c c d d
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
now using only the string ‘A’ by writting the corresponding number under its corresponding letter,this can be written as:
now certain floyd triangles are formed starting with length 4 which is the length of string ‘A’ and ending with 1.Now find the floyd triangle in which k is present.We can find that using the last terms of the floyd triangles as they from a series.In this case the series is,0,10,16,19,20.The ith term of this series is found by adding sigma(n-i-1) to the (i-1)th term where n is length of string ‘A’ and first term of this series is always 0.
k is present in the floyd triangle whose last term is greater than k. In this way the triangle is found.Now we just have to find the row in which k is present.Now take a variable ‘j’ which has value n-1 and ‘x’ which has last term of triangle.let l be be the number of lines of the required triangle that is found.Now k is present in the upper most row whose last term is greater than k.This can be achieved by subtracting l from x and decrementing j and l simultaneously.when x is less than k,then the row below is required.now the required answer is just printing j-k-1 index of string ‘A’.