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例如:
A[]={1,2,3}求B[]
B[0]=A[1]×A[2]=2×3=6
B[1]=A[0]×A[2]=1×3=3
B[2]=A[0]×A[1]=1×2=2
所以 B 数组为{6,3,2}
import java.util.Arrays;
public class Test52 {
public static double[] multiply(double[] data) {
if (data == null || data.length < 2) {
return null;
}
double[] result = new double[data.length];
// result[0]取1
result[0] = 1;
for (int i = 1; i < data.length; i++) {
// 第一步每个result[i]都等于于data[0]*data[1]...data[i-1]
// 当i=n-1时,此时result[n-1]的结果已经计算出来了【A】
result[i] = result[i -1] * data[i - 1];
}
// tmp保存data[n-1]*data[n-2]...data[i+1]的结果
double tmp = 1;
// 第二步求data[n-1]*data[n-2]...data[i+1]
// 【A】result[n-1]的结果已经计算出来,所以从data.length-2开始操作
for (int i = data.length - 2; i >= 0; i--) {
tmp *= data[i + 1];
result[i] *= tmp;
}
return result;
}
public static void main(String[] args) {
double[] array1 = {1, 2, 3, 4, 5};
System.out.println(Arrays.toString(multiply(array1))); // double expected[] = {120, 60, 40, 30, 24};
double[] array2 = {1, 2, 0, 4, 5};
System.out.println(Arrays.toString(multiply(array2))); // double expected[] = {0, 0, 40, 0, 0};
double[] array3 = {1, 2, 0, 4, 0};
System.out.println(Arrays.toString(multiply(array3))); // double expected[] = {0, 0, 0, 0, 0};
double[] array4 = {1, -2, 3, -4, 5};
System.out.println(Arrays.toString(multiply(array4))); // double expected[] = {120, -60, 40, -30, 24};
double[] array5 = {1, -2};
System.out.println(Arrays.toString(multiply(array5))); // double expected[] = {-2, 1};
}
}