Given n, find the nth number which is not a perfect square among natural numbers (1, 2, 3, 4, 5, 6, … )
Input : 3 Output : 5 First three non-square numbers are 2, 3 and 5 Input : 5 Output : 7 Input : 16 Output : 20
Looking at the problem statement we can come up to a straight-forward brute-force approach. We can start from n = 1, and start to check if each of them is a perfect square or not. So we can come up to the nth non-square number.
However, the above approach is very slow as it searches for each in every number smaller than the target each time.
We can observe that the series under consideration is 2, 3, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15, 17, … .
We can come upto the constant time formula for the nth number in this sequence, by inspection.
The correctness of the formula can be proved by the Principle of Mathematical Induction.
The implementation of the above formula is given below.
# Python3 program to find n-th
# non-square number.
# function to find the nth
# Non-Square Number
# conversion from int to long
# double is necessary in order
# to preserve decimal places
# after square root.
x = n;
# calculating the result
ans = x + math.floor(0.5 + math.sqrt(x));
# Driver code
# initializing the term number
n = 16;
# Print the result
print(“The”, n, “th Non-Square number is”,
# This code is contributed by mits
The 16th Non-Square number is 20
Time Complexity .
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