[WXM] LeetCode 397. Integer Replacement C++

397. Integer Replacement

Given a positive integer n and you can do operations as follow:

1.If n is even, replace n with n/2.
2.If n is odd, you can replace n with either n + 1 or n - 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

Approach

1.题目大意是当数字为偶数的时候只能进行除2操作，当数字为奇数的时候只能进行加1或减一操作，当数字变为1的时候需要多少次操作。这道题可以直接深搜即可，当数字为偶数的时候那就搜索加1和减1的情况，然后当数字为奇数的时候搜索除2的情况。

Code

class Solution {
public:
	int minn = INT_MAX;
	void DFS(long long n, int cnt) {
		if (cnt >= minn || n == 0)return;
		if (n == 1) {
			minn = min(minn, cnt);
			return;
		}
		if (n & 1) {
			DFS(n - 1, cnt + 1);
			DFS(n + 1, cnt + 1);
		}
		else {
			DFS(n >> 1, cnt + 1);
		}
	}
	int integerReplacement(int n) {
		DFS(n, 0);
		return minn;
	}
};