2. 对数组排序，使得a1<=a2>=a3<=a4>=... 也是很简单的O(n)，注意写的时候不用swap元素。。。

<span style="font-size:18px;">1.维护一个flag标志进行一次遍历就可以了</span>

int[] sortArray(int[] s){int n = s.length;boolean flag = true;int current = s[0];for (int i = 0; i < n-1; i++){if (((flag) &&(current > s[i+1])) || ((!flag) && (current < s[i+1])){s[i] = s[i+1];}else{s[i] = current;current = s[i + 1];}flag = !flag;}s[n-1] = current;return s;}