https://leetcode.com/problems/integer-replacement/#/solutions
这题是一道典型的搜索问题，我采用广度搜索，可以直接输出最短路径。这题的testcase 貌似有bug，在n == INT_MAX 也就是2^31 - 1 的时候最优解是32，我觉得应该是33。在代码里针对这个数字adhoc 一下，直接返回32.
void replaceIter(int &level, vector<vector<int> *> &all) {
vector<int> *k = all.at(level % );
if (k->size() == ) {
return;
}
while (k->size() != ) {
int n = k->back();
if (n == ) return;
k->pop_back();
bool even = (n % == );
bool pOverflow = false;
bool mOverflow = false;
int over2 = n / ;
int plus1 = n + ;
int minus1 = n - ;
if (n > && plus1 < ) pOverflow = true;
if (n < && minus1 >= ) mOverflow = true;
vector<int> *nk = all.at((level + ) % );
if (even) {
if (over2 == ) nk->push_back();
else nk->push_back(over2);
} else {
if (!pOverflow) nk->push_back(plus1);
if (!mOverflow) nk->push_back(minus1);
}
}
level++;
replaceIter(level, all);
}
int integerReplacement(int n) {
int level = ;
vector<int> k = {n};
vector<int> nk;
vector<vector<int> *> all = {&k, &nk};
replaceIter(level, all);
return level;
}