問題描述:
Find the contiguous subarray within an array (containing at least one number) which has the largest product.
For example, given the array [2,3,-2,4]
,
the contiguous subarray [2,3]
has the largest product = 6
.
解題思路:
首先想到的就是DP求解,第i位的最小乘積子串可以能是[0,i], [1,i]…… [i-1,i],[i,i]都可能。考慮到nums[i]可正可負,我們這樣吧問題分解:
1. 若nums[i]>0,f(i) = max(前i-1位的最大值*nums[i],nums[i]);
2. 若nums[i]<0,f(i) = max(前i-1位的最小值*nums[i],nums[i]);
因此我們是用兩個值,pMax,nMax分別表示當前的最大值與最小值。給出代碼:
int maxProduct(vector<int>& nums) {
if(nums.size() == 1) return nums[0];
int pMax = 0, nMax = 0, m = 0;
for(int i = 0; i<nums.size();i++){
if(nums[i]<0) swap(pMax, nMax);
pMax = max(pMax*nums[i], nums[i]);
nMax = min(nMax*nums[i], nums[i]);
m = max(m, pMax);
}
return m;
}