刷题152. Maximum Product Subarray
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一、题目说明
题目152. Maximum Product Subarray,给一列整数,求最大连续子序列,其乘积最大。难度是Medium!
二、我的解答
这个题目,用双重循环就可以了。
class Solution{
public:
int maxProduct(vector<int>& nums){
if(nums.size()<=1) return nums[0];
product = INT_MIN;
int len = nums.size();
for(int i=0;i<len;i++){
int p = nums[i];
if(p>product) product = p;
for(int t=i+1;t<len;t++){
p *= nums[t];
if(p>product) product = p;
}
}
return product;
}
private:
int product;
};
性能如下:
Runtime: 200 ms, faster than 6.16% of C++ online submissions for Maximum Product Subarray.
Memory Usage: 9.1 MB, less than 82.50% of C++ online submissions for Maximum Product Subarray.
三、优化措施
仔细再读读题目,一列整数,上述方法太“通用”,一次循环就可以了。
class Solution{
public:
//dp,其中dp[i]表示以第i个元素结尾的最大乘积
int maxProduct(vector<int>& nums){
if(nums.size()<=1) return nums[0];
dpMax = nums[0];
dpMin = nums[0];
maxProd = nums[0];
int len = nums.size();
for(int i=1;i<len;i++){
int preMax = dpMax;
dpMax = max(dpMin*nums[i],max(nums[i],dpMax*nums[i]));
dpMin = min(dpMin*nums[i],min(preMax*nums[i],nums[i]));
cout<<"i="<<i<<",dpMax="<<dpMax<<",dpMin="<<dpMin<<"
";
maxProd = max(dpMax,maxProd);
}
return maxProd;
}
private:
int dpMax;
int dpMin;
int maxProd;
};
Runtime: 16 ms, faster than 9.45% of C++ online submissions for Maximum Product Subarray.
Memory Usage: 9.1 MB, less than 75.00% of C++ online submissions for Maximum Product Subarray.
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