279. Perfect Squares

Medium

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 <= 10^4

解題

func numSquares(n int) int {
    dp := make([]int, n + 1)
    dp[0] = 0
    dp[1] = 1

    for i := 2; i <= n; i++ {
        dp[i] = math.MaxInt32
        for j := 1; i - j * j >= 0; j++ {
            dp[i] = min(dp[i], dp[i - j * j] + 1)
        }
    }

    return dp[n]
}

func min(a, b int) int {
    if a < b { return a }
    return b
}