void wiggleSort(vector<int>& nums) {
vector<int> m_nums = nums;
//find median
int median = -1;
if (nums.size() % 2 == 0)
median = (findKthElem(nums, nums.size() / 2) + findKthElem(nums, nums.size() / 2 + 1)) / 2;
else
median = findKthElem(nums, (nums.size() + 1) / 2);
//index rewriting
#define A(i) (nums[(2*(i)+1)%(nums.size()|1)])
//three-way sort
int i=0,j=0,k=nums.size()-1;
while(j<=k)
{
if(A(j)>median)//j往前行进的条件是A(j)>median 或 A(j)=median;j之前都>=median
{
swap(A(i),A(j));
i++,j++;
}
else if(A(j)<median)//k往后行进的条件是:A(j)<median,k之后都<median
{
swap(A(j),A(k));
k--;
}
else
j++;
}
}
// Find k'th element from A/B - idx starts from 0
double findKthElem(int A[], int m, int B[], int n, int k) {
if (m>n) return findKthElem(B, n, A, m, k);
if (!m) return B[k];
if (k == 0) return std::min(A[0], B[0]);
int pa = std::min((k+1)/2, m);
int pb = k+1-pa;
if (A[pa-1] > B[pb-1]) return findKthElem(A, pa, B+pb, n-pb, k-pb);
else return findKthElem(A+pa, m-pa, B, pb, k-pa);
}
double findMedianSortedArrays(int A[], int m, int B[], int n) {
if (!m) return (B[n/2]+B[(n-1)/2])/2.0;
if (!n) return (A[m/2]+A[(m-1)/2])/2.0;
if ((m+n)%2) {
return findKthElem(A, m, B, n, (m+n)/2);
}
else {
return (findKthElem(A, m, B, n, (m+n)/2)+
findKthElem(A, m, B, n, (m+n)/2-1)) / 2;
}
}
int findKthElem(vector<int> const &nums,int k)
{
int pivot = nums[rand()%nums.size()];
vector<int> lessThanK, geThanK;
for (auto num : nums)
{
if (num < pivot)
lessThanK.push_back(num);
else if (num>pivot)
geThanK.push_back(num);
}
int lt_pivot_num = lessThanK.size(), ge_pivot_num = geThanK.size();
if (k <= ge_pivot_num)
return findKthElem(geThanK, k);
else if (k > nums.size() - lt_pivot_num)
return findKthElem(lessThanK, k - (nums.size() - lt_pivot_num));
else
return pivot;
};
