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].

class Solution {
public:
    int reachNumber(int target) {
        if(target==0) return 0;
        if(target<0) target= -target;
        int len= (sqrt(1+8.0*target)-1)/2;
        int sum=len*(len+1)/2;
        if(sum == target) return len;
        int res=sum +(++len)- target;
        while(res%2)            
            res+=++len;
        return len;
    }
};