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# lintcode 31 · Partition Array (basic)

<https://www.lintcode.com/problem/31/description>

time: O(n)

space: O(1)

```java
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 left = 0;
        int right = nums.length - 1;
        while (left <= right) {
            while (left <= right && nums[left] < k) {
                left++;
            }
            while (left <= right && nums[right] >= k) {
                right--;
            }
            if (left <= right) {
                int temp = nums[left];
                nums[left] = nums[right];
                nums[right] = temp;
            }
        }
        return left;
    }
}
```