[LeetCode][279]perfect-squares
Content
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
Related Topics
Solution
1. 动态规划
Java
class Solution {
public int numSquares(int n) {
// 1 <= n <= 10⁴
// dp[i]表示数字i最少由几个平方数累加获取。
int[] dp = new int[n + 1];
Arrays.fill(dp, Integer.MAX_VALUE);
dp[0] = 0;
dp[1] = 1;
for (int i = 2; i <= n; i++) {
int j = (int) Math.sqrt(i);
while (j > 0) {
dp[i] = Math.min(dp[i], 1 + dp[i - j * j]);
j--;
}
}
return dp[n];
}
}