Given an integer n, return the least number of perfect square numbers that sum to n.
A perfect square is an integer that is the square of an integer; in other words, it is the product of some integer with itself. For example, 1, 4, 9, and 16 are perfect squares while 3 and 11 are not.
Example 1:
Input: n = 12
Output: 3
Explanation: 12 = 4 + 4 + 4.
Example 2:
Input: n = 13
Output: 2
Explanation: 13 = 4 + 9.
Constraints:
1 <= n <= 104
use std::cmp::min;
impl Solution {
pub fn num_squares(n: i32) -> i32 {
// make a dp array of size n + 1 and filled with 0
let mut dp = vec![n; n as usize + 1];
// set the first element to 0
dp[0] = 0;
// iterate from 1 to n
for i in 1..=n as usize {
// iterate from 1 to sqrt(i)
for j in 1..=(i as f64).sqrt() as usize {
// set dp[i] to the minimum of dp[i] and dp[i - j * j] + 1
dp[i] = min(dp[i], dp[i - j * j] + 1);
}
}
dp[n as usize]
}
}