整数拆分其积最大问题

$N = n_{1} + n_{2} + … + n_{k}$

若 $n_i\geq\ 5时，3 \times\ (n_i - 3) \geq\ n_i ，移项： 2 n_i \geq\ 9 $

$n_i = 4时，n_i = 2 + 2，其积：2 \times\ 2 $

最多两个2，原因：$2\times\ 2 \times\ 2 < 3 \times\ 3 $

说人话就是，将整数拆分为尽量多的3，最多2个2

题：25. 剪绳子

class Solution {
public:
    int maxProductAfterCutting(int length) {
        if (length <= 3) {
            return 1 * (length - 1);
        }
        int ans = 1;
        if (length % 3 == 1) {
            ans = 2 * 2;
            length -= 4;
        } else if (length % 3 == 2) {
            ans = 2, length -= 2;
        }
        int n = length / 3;
        while (n--) {
            ans *= 3;
        }
        return ans;
    }
};

class Solution {
public:
    int maxProductAfterCutting(int length) {
        if (length <= 3) {
            return 1 * (length - 1);
        }
        int ans = 1;
        if (length % 3 == 1) {
            ans = 2 * 2;
            length -= 4;
        } else if (length % 3 == 2) {
            ans = 2, length -= 2;
        }
        while (length > 0) {
            ans *= 3;
            length -= 3;
        }
        return ans;
    }
};