7.7 Design an algorithm to find the kth number such that the only prime factors are 3,5, and 7.
这道题跟之前LeetCode的那道Ugly Number II 丑陋数之二基本没有啥区别,具体讲解可参见那篇,代码如下:
class Solution {
public:
int getKthMagicNumber(int k) {
vector
int i3 = 0, i5 = 0, i7 = 0;
while (res.size() < k) {
int m3 = res[i3] * 3, m5 = res[i5] * 5, m7 = res[i7] * 7;
int mn = min(m3, min(m5, m7));
if (mn == m3) ++i3;
if (mn == m5) ++i5;
if (mn == m7) ++i7;
res.push_back(mn);
}
return res.back();
}
};
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