题目地址：https://leetcode.com/problems/reach-a-number/description/
题目描述
Youare standing at position 0 on an infinite number line. There is a goal at position target.
Oneach move, you can either go left or right. During the n-th move (starting from 1), you take n steps.
Return the minimum number of steps required to reach the destination.
Example 1:
Input: target = 3
Output: 2
Explanation:
On the first move we step from 0 to 1.
On the second step we step from 1 to 3.
Example 2:
Input: target = 2
Output: 3
Explanation:
On the first move we step from 0 to 1.
On the second move we step from 1 to -1.
On the third move we step from -1 to 2.
Note:
- target will be a non-zero integer in the range [-10^9, 10^9].
题目大意
每次走的步数是增加1步，方向是可以向左或者向右，求通过多少步之后能到达target。
解题方法
数学
非常不喜欢数学题，所以花花酱和Grandyang大神的帖子粘在这里了。
花花酱：https://zxi.mytechroad.com/blog/math/leetcode-754-reach-a-number/ Grandyang大神：http://www.cnblogs.com/grandyang/p/8456022.html
class Solution(object):
def reachNumber(self, target):
"""
:type target: int
:rtype: int
"""
target = abs(target)
k = 0
sum = 0
while sum < target:
k += 1
sum += k
d = sum - target
if d % 2 == 0:
return k
return k + 1 + (k % 2)
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C++版本如下：
class Solution {
public:
int reachNumber(int target) {
target = abs(target);
int k = 0;
int sum = 0;
while (sum < target) {
sum += (++k);
}
const int d = sum - target;
if (d % 2 == 0) return k;
return k + 1 + (k % 2);
}
};
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