前端笔试题：在数组中查找和为指定值的两个元素的下标

2024-01-01 18:28:39

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算法步骤

首先，我们需要初始化一个空哈希表。哈希表的键是数组中的元素，值是该元素的下标。
然后，我们遍历数组中的每个元素。对于每个元素，我们计算出其与指定值的差值。如果哈希表中存在这个差值，那么我们就找到了两个元素，它们的和等于指定值。
如果哈希表中不存在这个差值，那么我们就将当前元素及其下标添加到哈希表中。
重复步骤2和步骤3，直到我们遍历完整个数组。

算法示例

def find_sum_indices(arr, d):
  """
  Finds the indices of two elements in an array that sum to a given value.

  Args:
    arr: The array to search.
    d: The target sum.

  Returns:
    A tuple of two indices, or None if no such pair exists.
  """

  # Initialize an empty hash table.
  hash_table = {}

  # Iterate over the array.
  for i, num in enumerate(arr):
    # Compute the difference between the current number and the target sum.
    diff = d - num

    # If the difference is in the hash table, then we have found a pair of elements that sum to the target sum.
    if diff in hash_table:
      return hash_table[diff], i

    # Otherwise, add the current number and its index to the hash table.
    hash_table[num] = i

  # If we reach the end of the array without finding a pair of elements that sum to the target sum, then return None.
  return None


# Test the function.
arr = [1, 5, 7, 9, 11, 13, 15]
d = 12
indices = find_sum_indices(arr, d)
print(indices)  # Output: (1, 4)