資訊專欄INFORMATION COLUMN
摘要：復(fù)雜度思路找數(shù)組里面的等差數(shù)列的個數(shù)。想法是如果一開始三個數(shù)就滿足是等差數(shù)列的話，就在當(dāng)前已有的數(shù)目上不斷的累加的結(jié)果。
Leetcode[413] Arithmetic Slices
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.
A = [1, 2, 3, 4] return: 3, for 3 arithmetic slices in A: [1, 2, 3], [2, 3, 4] and [1, 2, 3, 4] itselfDP
復(fù)雜度
O(N)
思路
找數(shù)組里面的等差數(shù)列的個數(shù)。想法是如果一開始三個數(shù)就滿足是等差數(shù)列的話，就在當(dāng)前已有的數(shù)目上不斷的累加count的結(jié)果。然后更新sum。
代碼
public int numberOfArithmeticSlices(int[] nums) {
int cur = 0, sum = 0;
for(int i = 2; i < nums.length; i ++) {
if(nums[i] == nums[i - 1] && nums[i - 1] == nums[i - 1]) {
cur += 1;
sum += cur;
}
else {
cur = 0;
}
}
return sum;
}
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