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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0201_0300.s0279_perfect_squares;

// #Medium #Top_Interview_Questions #Dynamic_Programming #Math #Breadth_First_Search
// #Dynamic_Programming_I_Day_21 #2022_07_06_Time_1_ms_(100.00%)_Space_40.2_MB_(99.44%)

/**
 * 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 <= 10⁴
**/
public class Solution {
    private boolean validSquare(int n) {
        int root = (int) Math.sqrt(n);
        return root * root == n;
    }

    public int numSquares(int n) {
        if (n < 4) {
            return n;
        }
        if (validSquare(n)) {
            return 1;
        }
        while ((n & 3) == 0) {
            n >>= 2;
        }
        if ((n & 7) == 7) {
            return 4;
        }
        int x = (int) Math.sqrt(n);
        for (int i = 1; i <= x; i++) {
            if (validSquare(n - i * i)) {
                return 2;
            }
        }
        return 3;
    }
}