Ugly Number Sequel - Amazon Top Interview Questions
Problem Statement :
Consider a sequence of sorted integers whose prime factors only include 2, 3 or 5. The first few terms are 1, 2, 3, 4, 5, 6, 8, 9, 10. Given an integer n, return the nth (0-index) term of the sequence. Constraints 0 ≤ n ≤ 100,000 Example 1 Input n = 5 Output 6 Explanation Since the first six terms are 1, 2, 3, 4, 5, 6.
Solution :
Solution in C++ :
int solve(int n) {
vector<int> dp(n + 1, 1);
int p = 0, q = 0, r = 0;
for (int i = 1; i <= n; i++) {
dp[i] = min(min(dp[p] * 2, dp[q] * 3), dp[r] * 5);
if (dp[i] == dp[p] * 2) p++;
if (dp[i] == dp[q] * 3) q++;
if (dp[i] == dp[r] * 5) r++;
}
return dp[n];
}
Solution in Python :
class Solution:
def solve(self, n):
l = [1]
i2, i3, i5 = 0, 0, 0
while n:
x2, x3, x5 = 2 * l[i2], 3 * l[i3], 5 * l[i5]
mn = min(x2, x3, x5)
i2 += x2 == mn
i3 += x3 == mn
i5 += x5 == mn
l.append(mn)
n -= 1
return l[-1]
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