编程之美2.13子数组的最大乘积Java版

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package Test;

/**
*
* 2.13 子数组的最大乘积
*/
public class SearchArrayMaxMultiply {

public static void main(String[] args) {
int[] arry = new int[]{-2, -1, -8, -5, -7, -12};
//解法一
int num1 = search_max_multiply1(arry);
System.out.println("最大乘积=" + num1);
//解法二
int num2 = search_max_multiply2(arry);
System.out.println("最大乘积=" + num2);
}

private static int search_max_multiply1(int[] arry) {
int[] before = new int[arry.length];
int[] after = new int[arry.length];

int num = arry.length - 1;

before[0] = 1;
for (int i = 1; i < arry.length; i++) {
before[i] = before[i - 1] * arry[i - 1];
}
after[num] = 1;
for (int i = num - 1; i >= 0; i--) {
after[i] = after[i + 1] * arry[i + 1];
}
int max = before[0] * after[0];
for (int i = 1; i <= num; i++) {
int tmp = before[i] * after[i];
if (tmp > max) {
max = tmp;
}
}

return max;
}

private static int search_max_multiply2(int[] arry) {
int max = 1;
int p_num = 0;
int n_num = 0;
int z_num = 0;
int min_p = 0;//最小正数
int min_n = 0;//最小负数
int max_n = 0;//最大负数
for (int i = 0; i < arry.length; i++) {
if (arry[i] > 0) {
if (arry[i] < min_p || min_p == 0) {
min_p = arry[i];
}
p_num++;
} else if (arry[i] < 0) {
if (arry[i] < min_n) {
min_n = arry[i];
}
if (arry[i] > max_n || max_n == 0) {
max_n = arry[i];
}
n_num++;
} else {
z_num++;
}
}
if (z_num >= 2) {
max = 0;
return max;
} else {
if (z_num == 1) {//只有一个0
//去掉0的乘积为正数,即有偶数个负数，最大乘积是去掉0后的子数组的乘积
if (n_num % 2 == 0) {
for (int i : arry) {
if (i != 0) {
max *= i;
}
}
} else {//去掉0的乘积为负数,即有奇数个负数,最大乘积是0
max = 0;
}
} else {//如果没有0
if (n_num % 2 == 0) {//如果完整数组的乘积是个正数,即有偶数个负数
if (p_num > 0) {//如果存在正数，最大乘积是去掉最小正数后的子数组的乘积
for (int i : arry) {
if (i != min_p) {
max *= i;
}
}
} else {//如果不存在正数,最大乘积是去掉最小负数后的子数组的乘积
for (int i : arry) {
if (i != min_n) {
max *= i;
}
}
}
} else {//如果完整数组的乘积是个负数，即有奇数个负数。则最大乘积是去掉最大负数后的子数组的乘积
for (int i : arry) {
if (i != max_n) {
max *= i;
}
}
}
}
}
return max;
}
}