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integer-replacement.cpp
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integer-replacement.cpp
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// Time: O(logn)
// Space: O(1)
// Iterative solution.
class Solution {
public:
int integerReplacement(int n) {
if (n == 2147483647) {
return 2 + integerReplacement(n / 2 + 1);
}
int result = 0;
while (n != 1) {
const auto b = n & 3;
if (n == 3) {
--n;
} else if (b == 3) {
++n;
} else if (b == 1) {
--n;
} else {
n /= 2;
}
++result;
}
return result;
}
};
// Time: O(logn)
// Space: O(logn)
// Recursive solution
class Solution2 {
public:
int integerReplacement(int n) {
if (n == 2147483647) {
return 2 + integerReplacement(n / 2 + 1);
}
if (n < 4) {
switch (n % 4) {
case 0: case 1: return 0;
case 2: return 1;
case 3: return 2;
}
}
switch (n % 4) {
case 0: case 2: return integerReplacement(n / 2) + 1;
case 1: return integerReplacement((n - 1) / 4) + 3;
case 3: return integerReplacement((n + 1) / 4) + 3;
}
return 0;
}
};