Decrease Elements To Make Array Zigzag LeetCode solution in Java

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class Solution {
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  /*
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      firstly, check elements in odd indices are greater than its neighbours.
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      if not, decrease its neigbours and update the cost.
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      do same thing for even indices, because there can be two combinations as indicated in question.
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  */
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  private int calculateCost(int[] nums, int start) {
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    int res = 0;
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    int n = nums.length;
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    int[] arr = Arrays.copyOf(nums, nums.length); // nums array will be modified, so copy it.
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    for (int i = start; i < n; i += 2) {
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      int prev = (i == 0) ? Integer.MIN_VALUE : arr[i - 1];
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      int cur = arr[i];
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      int next = (i == n - 1) ? Integer.MIN_VALUE : arr[i + 1];
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      if (prev < cur && next < cur) continue;
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      if (prev >= cur) {
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        res += prev - cur + 1;
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        arr[i - 1] = cur - 1;
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      }
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      if (next >= cur) {
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        res += next - cur + 1;
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        arr[i + 1] = cur - 1;
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      }
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    }
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    return res;
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  }
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  public int movesToMakeZigzag(int[] nums) {
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    return Math.min(calculateCost(nums, 0), calculateCost(nums, 1));
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  }
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}