324. Wiggle Sort II

这个题真是做得我想打人了。我生起气来连自己都打。

一开始quick select没啥可说的。但是in place把老命拼了都没想出来。。

看网上的答案是3 partition，MAP式子一看就由衷地反胃。。

老子不管了，就O(n)。。

public class Solution
{
    public void wiggleSort(int[] nums)
    {
        if(nums.length <= 1 ) return;
        if(nums.length == 2)
        {
            if(nums[0] > nums[1]) swap(0,1,nums);
            return;
        }

        //start of larger half
        int m = (nums.length+1)/2;

        int mVal = nums[quickSelect(nums,m,0,nums.length-1)];

        int[] res = new int[nums.length];

        int a = 0, b = nums.length-1;
        for(int i = 0; i < res.length;i++)
        {
            if(nums[i] < mVal)
            {
                res[a] = nums[i];
                a++;
            }
            else if(nums[i] > mVal)
            {
                res[b] = nums[i];
                b--;
            }

        }

        while(a < m) res[a++] = mVal;
        while(b >= m) res[b--] = mVal;
        //System.out.println(a + " " + b + " " + m + " " + mVal);
        b = nums.length-1;
        a-=1;
        for(int i = 0; i < nums.length;i++)
        {

            if(i%2 == 0)
            {
                nums[i] = res[a];
                a--;

            }
            else
            {
                nums[i] = res[b];
                b--;

            }
        }

        return;

    }

    public int quickSelect(int[] nums, int m, int L, int R)
    {
        int pIndex = awesomePick(L,R,nums);
        int pVal = nums[pIndex];

        swap(R,pIndex,nums);
        int tempIndex = L;
        for(int i = L; i < R;i++)
        {
            if(nums[i] <= pVal) swap(i,tempIndex++,nums);
        }
        swap(tempIndex,R,nums);

        if(tempIndex == m) return tempIndex;
        else if(tempIndex < m) return quickSelect(nums,m,tempIndex+1,R);
        else return quickSelect(nums,m,L,tempIndex-1);

    }

    public void swap(int a, int b, int[] nums)
    {
        int temp = nums[a];
        nums[a] = nums[b];
        nums[b] = temp;
    }

    public int awesomePick(int L, int R, int[] nums)
    {
        int a = nums[L];
        int b = nums[R];
        int M = L+(R-L)/2;
        int c = nums[M];

        if( a > b )
        {
            if( b > c ) return R;
            else if(a > c) return M;
            else return L;

        }
        //b > a
        else
        {
            if(a > c) return L;
            else if(b > c) return M;
            else return R;
        }
    }
}