寻找数组中轴索引

• 2019 年 11 月 8 日
• 筆記

将 pivot 索引定义为：左边的数字之和等于索引右边的数字之和。

Input:  nums = [1, 7, 3, 6, 5, 6]  Output: 3  Explanation:  1 + 7 + 3 = 5 + 6    Input:  nums = [1, 2, 3]  Output: -1  Explanation:  There is no index that satisfies the conditions in the problem statement.

Note:

• The length of nums will be in the range [0, 10000].
• Each element nums[i] will be an integer in the range [-1000, 1000].

关键点

• 动态规划
• 数组的和 – 中轴数 = 中轴数左边数组的和 * 2

解答

func findPivot(_ array: [Int]) -> Int {      // 数组和      let sum = array.reduce(0, +)      // 左侧数组和      var leftSum = 0      for (key, value) in array.enumerated() {          if sum - value == leftSum * 2 {              return key          }          leftSum += value      }      return -1  }    let array = [1, 7, 3, 6, 5, 6]  search(array) // 3

Reference:

• 找到数组中左右两边的和相等的 pivot 的下标 Find Pivot Index

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