Partition Array

Med 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.

Thoughts

和sort colors 类似，是一道3-way partition的题。

Code

public class Solution {
    /** 
     *@param nums: The integer array you should partition
     *@param k: As description
     *return: The index after partition
     */
    public int partitionArray(int[] nums, int k) {
        if (nums.length == 0) {
            return 0;
        }
        int start = 0, other = start, end = nums.length - 1;
        while (start <= end) {
            if (nums[start] < k) {
                swap(nums, start, other);
                start++;
                other++;
            } else if (nums[start] == k) {
                start++;
            } else {
                swap(nums, start, end);
                end--;
            }
        }

        return other;
    }

    private void swap(int[] nums, int i, int j) {
        int tmp = nums[i];
        nums[i] = nums[j];
        nums[j] = tmp;
    }
}

Analysis

TC: O(n)