算法系列：
class Solution {
public int[] productExceptSelf(int[] nums) {
int[] answer= new int[nums.length];
int p = 1, q = 1;
for (int i = 0; i < nums.length; i++) {
answer[i] = p;
p *= nums[i];
}
for (int i = nums.length - 1; i > 0 ; i--) {
q *= nums[i];
res[i - 1] *= q;
}
return answer;
}
}
