java 324. Wiggle Sort II（＃）。java

Posted 2021-05-08

public class Solution {
    public void wiggleSort(int[] nums) {  
        int[] sorted = nums.clone();  
        Arrays.sort(sorted);  
        int mid = (nums.length-1) / 2;  
        for(int i=0, j=mid, k=nums.length-1; i<nums.length; i+=2, j--, k--) {  
            nums[i] = sorted[j];  
            if (i+1<nums.length) nums[i+1] = sorted[k];  
        }  
    }  
}

public class Solution {
    private int findMedian(int[] nums) {
        return findKthSmallest(nums, 0, nums.length - 1, (nums.length + 1) / 2);
    }
    private int findKthSmallest(int[] nums, int start, int end, int k) {
        if (start == end) {
            return nums[start];
        }
        
        int pivot = nums[start + (end - start) / 2];
        int left = start;
        int right = end;
        while (left <= right) {
            while (left <= right && nums[left] < pivot) {
                left++;
            }
            while (left <= right && nums[right] > pivot) {
                right--;
            }
            if (left <= right) {
                int temp = nums[left];
                nums[left] = nums[right];
                nums[right] = temp;
                left++;
                right--;
            }
        }
        if (start + k - 1 <= right) {
            return findKthSmallest(nums, start, right, k);
        } else if (start + k - 1 >= left) {
            return findKthSmallest(nums, left, end, k - (left - start));
        } else {
            return pivot; // return nums[start + k - 1];
        }
    }
    private int getIdx(int idx, int n) {
        return (1 + 2 * idx) % (n | 1);
    }
    private void swap(int[] nums, int i, int j) {
        int temp = nums[i];
        nums[i] = nums[j];
        nums[j] = temp;
    }
    public void wiggleSort(int[] nums) {
        int median = findMedian(nums);
        int n = nums.length;
        int left = 0, i = 0, right = n - 1;
        while (i <= right) {
            int cur = nums[getIdx(i, n)];
            if ( cur > median) {
                swap(nums, getIdx(i++, n), getIdx(left++, n));
            } else if (cur < median) {
                swap(nums, getIdx(i, n), getIdx(right--, n));
            } else {
                i++;
            }
        } 
    }
}