1.题目：​​https://leetcode-cn.com/problems/squares-of-a-sorted-array/​​

2.思路

（1）用sort，过于简单了
（2）归并排序的思想

3.代码

https://leetcode-cn.com/problems/squares-of-a-sorted-array/solution/yong-gui-bing-si-xiang-ji-ke-by-daniel_shwei/
方法1：
class Solution {
public:
    vector<int> sortedSquares(vector<int>& A) {
        for (int i=0;i<A.size();i++)
            A[i]*=A[i];
        sort(A.begin(),A.end());
        return A;
    }
};

方法2：
class Solution {
public:
    vector<int> sortedSquares(vector<int>& A) {
        int leth=A.size();
        int i=0,j=leth-1,k=leth;
        vector<int> B(leth);
        while (k>0)
        {
            int x=A[i]*A[i];
            int y=A[j]*A[j];
            if (x>y)
            {
                B[--k]=x;
                i++;
            }
            else
            {
                B[--k]=y;
                j--;
            }
        }
        return B;
    }
};

改进方法2
class Solution {
public:
    vector<int> sortedSquares(vector<int>& A) {
        int leth=A.size()-1;
        int i=0,j=leth,k=leth;
        vector<int> B(leth+1);
        while (k>=0)
        {
            int x=A[i]*A[i];
            int y=A[j]*A[j];
            if (x>y)
            {
                B[k--]=x;
                i++;
            }
            else
            {
                B[k--]=y;
                j--;
            }
        }
        return B;
    }
};