413. Arithmetic Slices

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Problem:

A sequence of number is called arithmetic if it consists of at least three elements and if the difference between any two consecutive elements is the same.

For example, these are arithmetic sequence:

1, 3, 5, 7, 9
7, 7, 7, 7
3, -1, -5, -9

The following sequence is not arithmetic.

1, 1, 2, 5, 7

A zero-indexed array A consisting of N numbers is given. A slice of that array is any pair of integers (P, Q) such that 0 <= P < Q < N.

A slice (P, Q) of array A is called arithmetic if the sequence:
A[P], A[p + 1], ..., A[Q - 1], A[Q] is arithmetic. In particular, this means that P + 1 < Q.

The function should return the number of arithmetic slices in the array A.

Example:

A = [1, 2, 3, 4]

return: 3, for 3 arithmetic slices in A: [1, 2, 3], [2, 3, 4] and [1, 2, 3, 4] itself.

思路：

Solution (C++):

int numberOfArithmeticSlices(vector<int>& A) {
    int n = A.size();
    if (n < 3)  return 0;
    vector<int> dp(n, 0);
    if (A[2]-A[1] == A[1]-A[0])  dp[2] = 1;
    int res = dp[2];
    for (int i = 3; i < n; ++i) {
        if (A[i] + A[i-2] == 2*A[i-1])
            dp[i] = dp[i-1] + 1;
        res += dp[i];
    }
    return res;
}

性能：

Runtime: 0 ms??Memory Usage: 6.5 MB

思路：

Solution (C++):

性能：

Runtime: ms??Memory Usage: MB

413. Arithmetic Slices

标签：solution   wing   enc   sage   follow   ice   sequence   ret   diff   

原文地址：https://www.cnblogs.com/dysjtu1995/p/12684736.html