Given an array nums of integers and an int k, partition the array (i.e move the elements in "nums") such that: All elements < k are moved to the left. All elements >= k are moved to the right

Return the partitioning index, i.e the first index i nums[i] >= k. 其实就是quicksort的第一步

public class Solution {
    /**
     * @param nums: The integer array you should partition
     * @param k: An integer
     * @return: The index after partition
     */
    public int partitionArray(int[] nums, int k) {
        // write your code here
        int start = 0;
        int end = nums.length - 1;

        while(start <= end) {
            while(start <= end && nums[start] < k) start++;

            while(start <= end && nums[end] >= k) end--;

            if(start <= end) {
                int temp = nums[start];
                nums[start] = nums[end];
                nums[end] = temp;

                start++;
                end--;
            }  
        }
        return start;
    }
}


第二次做
public class Solution {
    /**
     * @param nums: The integer array you should partition
     * @param k: An integer
     * @return: The index after partition
     */
    public int partitionArray(int[] nums, int k) {
        int p = 0;
        for(int i = 0; i < nums.length; i++) {
            if(nums[i] < k) {
                int temp = nums[p];
                nums[p] = nums[i];
                nums[i] = temp;
                p++;
            } 
        }
        return p;
    }
}