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/**
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 * @param {number[]} nums
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 * @return {number}
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 */
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var wiggleMaxLength = function (nums) {
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  //two pass
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  //assume we start with positive or start with negative
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  //choose the longest of the two
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  return Math.max(helper(nums, true), helper(nums, false));
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};
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const helper = (nums, start) => {
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  let l = 0;
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  let r = 1;
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  let res = nums.length;
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  let sign = start;
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  while (r < nums.length) {
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    //if sign are what we expected, just flip the sign
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    if ((sign && nums[r] > nums[l]) || (!sign && nums[r] < nums[l])) {
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      sign = !sign;
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    }
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    //if sign aren't what we expected then we "remove" one
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    //if we want positive then we remove the bigger number to give us a better chance of getting positive
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    //if we want negative we remove the smaller number go give us a chance of getting a negative
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    // want negative but nums[r] - nums[l] = positive   => remove nums[l]
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    // want positive but nums[r] - nums[l] = negative   => remove nums[l]
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    //it just so happens that the number we want to remove will always be nums[l], so we don't have to do anything special
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    else {
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      res--;
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    }
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    l++;
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    r++;
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  }
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  return res;
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};