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

References

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