628. Maximum Product of Three Numbers--找最大乘積

Given an integer array, find three numbers whose product is maximum and output the maximum product.

Example 1:

Input: [1,2,3]
Output: 6

Example 2:

Input: [1,2,3,4]
Output: 24

Note:

1. The length of the given array will be in range [3,104] and all elements are in the range [-1000, 1000].
2. Multiplication of any three numbers in the input won't exceed the range of 32-bit signed integer.

在數組裏找三個數，使乘積最大即可。想到的方法是先排序，然後按照正數有1個還是其他多個去找最大值，最大值出現的組合可能是：前2個數字和最後一個數字，最後三個數字，代碼有點冗長：

Arrays.sort(nums);
		int len = nums.length;
		for(int j=0;j<len;j++){
		System.out.println(nums[j]);}
		int count=0;
		
		int i=len-1;
		int res = Integer.MIN_VALUE;
		
		while(i>=0){
			if(nums[i]>0){count++;}
			if(nums[i]<=0) {break;}
			i--;
		}
		if(count!=1){
			res = Math.max(res,nums[len-1]*nums[len-2]*nums[len-3]);
			res = Math.max(res, nums[len-1]*nums[0]*nums[1]);
		}
		if(count==1){
			res = Math.max(res,nums[len-1]*nums[0]*nums[1]);
		}
		return res;

結果，其實這樣就行了==：

int len = nums.length;
		Arrays.sort(nums);
		int a = nums[0]*nums[1]*nums[len-1];
		int b = nums[len-2]*nums[len-3]*nums[len-1];
		return Math.max(a, b);