LeetCode: Arithmetic Slices

先找到差值相等的連續數，大於2的話就能夠加，注意這裏加的是1+2+3+。。。＋num-1的值，即num*(num-1)/2

 1 public class Solution {
 2     public int numberOfArithmeticSlices(int[] A) {
 3         if (A.length < 3) return 0;
 4         int[] diff = new int[A.length-1];
 5         for (int i = 0; i < diff.length; i++) {
 6             diff[i] = A[i+1] - A[i];
 7         }
 8         int num = 1;
 9         int ans = 0;
10         int diffNum = diff[0];
11         for (int i = 1; i < diff.length; i++) {
12             if (diff[i] == diffNum) num++;
13             else {
14                 diffNum = diff[i];
15                 if (num > 1) {
16                     ans += num * (num-1) / 2;
17                 }
18                 num = 1;
19             }
20         }
21         if (num > 1) {
22             ans += num * (num-1) / 2;
23         }
24         return ans;
25     }
26 }