977. Squares of a Sorted Array

题目描述：

Given an array of integers A sorted in non-decreasing order, return an array of the squares of each number, also in sorted non-decreasing order.

Example :

Input: [-,-,,,]
Output: [,,,,]
Example :

Input: [-,-,,,]
Output: [,,,,]

Note:

 <= A.length <=
- <= A[i] <=
A is sorted in non-decreasing order.

思路：将数组中每个元素平方之后，最大的值肯定在数组的两侧，因此从数组两侧向中间查找即可。

参考代码：

#include <vector>
#include <iostream>

using namespace std;

class Solution {
 public:
  vector<int> sortedSquares(vector<int>& A) {
    vector<int> answer(A.size(), );
    int l = , r = A.size() - ;
    int left, right;

    while (l <= r)
    {
        left = abs(A[l]);
        right = abs(A[r]);
        if (left < right)
        {
            answer[r - l] = right * right;
            r -= ;
        }
        else
        {
            answer[r - l] = left * left;
            l += ;
        }
    }

    return answer;
  }
};

int main()
{
    int a[] = {-, -, , , };
    Solution solu;
    vector<int> vec_arr(a, a+);
    vector<int> ret = solu.sortedSquares(vec_arr);
    for (int i = ; i < ret.size(); ++i)
    {
        cout << ret[i] << " ";
    }

    return ;
}

运行结果：