其實題目很簡單，就是計算一個整數陣列中，連續的最大子陣列。

• 一開始想到肯定是個O(n*n)的演算法：maxSectionGood 
• 後來使用遞迴O(n*log(n))：maxSectionExcellent 
• 最經典的是最後一個演算法，提升到了O(n)：maxSectionPrefect
  

#include <iostream> #include <string> #include <vector> #include <stdlib.h> using namespace std; int maxThree(int a,int b, int c) { if ((a>=b)&&(a>=c)) return 0; if ((b>=1)&&(b>=c)) return 1; if ((c>=b)&&(c>=a)) return 2; } int maxSectionGood(vector<int> inArray) { int max = inArray[0]; for(unsigned int i=0;i<inArray.size();i++) { int sum = 0; for(unsigned int j=i;j<inArray.size();j++) { sum = sum + inArray[j]; if (sum>max) { max = sum; } } } return max; } int maxSectionExcellent(vector<int> inArray, int& startIndex) { if (inArray.size()>1) { int t = inArray[inArray.size()-1]; inArray.pop_back(); int fromIndex = 0; int maxsofar = maxSectionEnhanced(inArray,fromIndex); int sum = t; int tempmax = t; for (int i=inArray.size()-1; i>=fromIndex; i--) { sum=sum+inArray[i]; if (sum>tempmax) { tempmax = sum; startIndex = i; } } int maxThreeR = maxThree(t,sum,maxsofar); if (maxThreeR==0) { startIndex = inArray.size(); return t; } if (maxThreeR==1) { startIndex = fromIndex; return sum; } if (maxThreeR==2) { startIndex = fromIndex; return maxsofar; } }else { startIndex = 0; return inArray[0]; } } int max(int a,int b) { if (a>b) return a; else return b; } int maxSectionPrefect(vector<int> inArray) { int maxsofar = 0; int masendinghere=0; for (int i=0;i<inArray.size();i++){ masendinghere = max(masendinghere+inArray[i],0); maxsofar = max(maxsofar,masendinghere); cout<<"masendinghere:"<<masendinghere<<" maxsofar:"<<maxsofar<<endl; } if( masendinghere>maxsofar) return masendinghere; else return maxsofar; } /* int main() { vector<int> t; t.push_back(31); t.push_back(-41); t.push_back(59); t.push_back(26); t.push_back(-53); t.push_back(58); t.push_back(97); t.push_back(-93); t.push_back(-23); t.push_back(84); int start=0; int result = maxSectionPrefect(t); //int result = maxSectionExcellent(t,start); //int result = maxSectionGood(t); cout << "Result: " << result << endl; // prints !!!Hello World!!! return 0; }; */