# Partition Array by Odd and Even

Partition an integers array into odd number first and even number second.

**Example**

Given`[1, 2, 3, 4]`, return`[1, 3, 2, 4]`

分析

对撞指针，quick select，不必递归

答案

```
public class Solution {
    /**
     * @param nums: an array of integers
     * @return: nothing
     */
    public void partitionArray(int[] nums) {
        // write your code here;
        if(nums == null || nums.length == 0)
            return;
        int left = 0, right = nums.length - 1, pivot = nums[left];
        while(left < right){
            while(left < right && nums[right] % 2 == 0){
                right --;
            }
            nums[left] = nums[right];
            while(left < right && nums[left] % 2 == 1){
                left ++;
            }
            nums[right] = nums[left];

        }
        nums[left] = pivot;
    }
}
```
