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class Solution {
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  public void sortColors(int[] nums) {
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    int zeroIndex = 0, twoIndex = nums.length - 1, i = 0;
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    while (i <= twoIndex) {
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      if (nums[i] == 0) swap(nums, zeroIndex++, i++);
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      else if (nums[i] == 2) swap(nums, twoIndex--, i);
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      else i++;
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    }
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  }
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  public void swap(int[] nums, int i, int j) {
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    int temp = nums[i];
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    nums[i] = nums[j];
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    nums[j] = temp;
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  }
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}