题解 | #子数组最大乘积#

因为存在负数 所以需要维护一个最小乘积minDp

维护一个最大乘积maxDp

    public double maxProduct(double[] arr) {
             int len = arr.length;
             if (arr == null || len == 0){
                 return  (double) 0.0;
             }
             double[] maxDp = new double[len];
             double[] minDp  = new double[len];
             System.arraycopy(arr,0,maxDp,0,len);
              System.arraycopy(arr,0,minDp,0,len);
        
        for (int i = 1; i < len; i++) {
                double num = arr[i];
                maxDp[i] = Math.max(maxDp[i-1]*num,Math.max(num,minDp[i-1]*num));
                minDp[i] = Math.min(minDp[i-1]*num,Math.min(num,maxDp[i-1]*num));
        }
        double  maxProduct = maxDp[0];
        for (int i = 1; i < len; i++) {
            maxProduct = Math.max(maxProduct,maxDp[i]);
        }
        return  maxProduct;
    }
}