4. Adjust the array order so that odd numbers precede even numbers

Double pointer

 public int[] exchange(int[] nums) {
       int left = 0, right = nums.length - 1;
        while(left <= right){
            while(left <= right && nums[left] % 2 == 1)
                left++;
            while(left <= right && nums[right] % 2 == 0)
                right--;
            if(left > right)
                break;
            int tmp = nums[left];
            nums[left] = nums[right];
            nums[right] = tmp;
        }
        return nums;
    }