Given a positive integer n and you can do operations as follow:
- If n is even, replace n with
n/2
. - If n is odd, you can replace n with either
n + 1
orn - 1
.
What is the minimum number of replacements needed for n to become 1?
Example 1:
Input: 8 Output: 3 Explanation: 8 -> 4 -> 2 -> 1
Example 2:
Input: 7 Output: 4 Explanation: 7 -> 8 -> 4 -> 2 -> 1 or 7 -> 6 -> 3 -> 2 -> 1解题步骤:
1、如果是两个挨着的1,而且当前数不等于3,采取+1处理,同时count++。
2、如果当前数最后一位是1,得多一步处理掉最后一位的操作,count+1。
3、把n除以二,count+1。
代码如下:
public class Solution {
public int integerReplacement(int n) {
if (n < 1) return 0;
int count = 0;
while (n != 1) {
if ((n & 3) == 3 && n != 3) {
n = n + 1;
count ++;
}
if ((n & 1) == 1) {
count ++;
}
n = n >>> 1;
count ++;
}
return count;
}
}
更易读的代码如下:
public int integerReplacement(int n) {
int c = 0;
while (n != 1) {
if ((n & 1) == 0) {
n >>>= 1;
} else if (n == 3 || ((n >>> 1) & 1) == 0) {
--n;
} else {
++n;
}
++c;
}
return c;
}