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class NumArray {
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  int[] prefix;
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  public NumArray(int[] nums) {
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    int n = nums.length;
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    prefix = new int[n];
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    prefix[0] = nums[0];
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    for (int i = 1; i < n; i++) {
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      prefix[i] = nums[i] + prefix[i - 1];
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    }
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  }
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  public int sumRange(int left, int right) {
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    if (left == 0) {
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      return prefix[right];
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    }
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    return prefix[right] - prefix[left - 1];
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  }
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}