leetcode238除自身以外数组的乘积

leetcode238
思路：左边的乘积创建数组保存，右边的乘积创建数组保存，ans = 左边*右边

常规代码：

int[] p;
    int[] q;
    public int[] productExceptSelf(int[] nums) {
        if(nums.length==0){
            return new int[]{};
        }
        p = new int[nums.length];
        q = new int[nums.length];
        p[0] = nums[0];
        q[nums.length-1] = nums[nums.length-1];
        for(int i = 1;i<nums.length;i++){
            p[i] = p[i-1]*nums[i];
        }
        for(int i = nums.length-2;i>=0;i--){
            q[i] = q[i+1]*nums[i];
        }
        int[] output = new int[nums.length];
        for(int i = 0;i<output.length;i++){
            if(i==0){
                output[i] = q[i+1];
            }
            else if(i== nums.length-1){
                output[i] = p[i-1];
            }
            else {
                output[i] = p[i-1]*q[i+1];
            }

        }
        return output;
    }

优化代码：
思路：同上，优化了空间

public int[] productExceptSelf(int[] nums) {
        if(nums.length==0){
            return new int[]{};
        }
        int[] output = new int[nums.length];
        int k = 1;
        for(int i = 0;i<output.length;i++){
            output[i] = k;
            k*=nums[i];
        }
        k = 1;
        for(int i = output.length-1;i>=0;i--){
            output[i]*=k;
            k*=nums[i];
        }
        return output;
    }