（算法）最大子数组和以及最大子矩阵和

#include<iostream>
#include<vector>

using namespace std;

int MaxSubArraySum_1(const vector<int> &arr){
    int n=arr.size();
    if(n==0)
        return 0;
    int sum=arr[0];
    int max=arr[0];
    for(int i=1;i<n;i++){
        if(sum>=0)
            sum+=arr[i];
        else
            sum=arr[i];
        if(sum>max)
            max=sum;
    }
    return max;
}

int MaxSubArraySum_2(const vector<int> &arr){
    int n=arr.size();
    if(n==0)
        return 0;
    vector<int> maxSub(n);
    maxSub[0]=arr[0];
    int max=arr[0];
    for(int i=1;i<n;i++){
        maxSub[i]=(maxSub[i-1]>0)?(maxSub[i-1]+arr[i]):arr[i];
        if(max<maxSub[i])
            max=maxSub[i];
    }
    return max;
}

int MaxSubMatrixSum(const vector<vector<int> > &arr){
    int m=arr.size();
    int n=arr[0].size();
    vector<vector<int> > total(m,vector<int>(n,0));

    for(int i=0;i<n;i++)
        total[0][i]=arr[0][i];

    for(int i=1;i<m;i++){
        for(int j=0;j<n;j++){
            total[i][j]=total[i-1][j]+arr[i][j];
        }
    }

    int max=-1000;
    vector<int> result(n);
    for(int i=0;i<m;i++){
        for(int j=i;j<m;j++){
            for(int f=0;f<n;f++){
                if(i==0)
                    result[f]=total[j][f];
                else
                    result[f]=total[j][f]-total[i-1][f];
            }        

            int maximal=MaxSubArraySum_2(result);
            if(maximal>max)
                max=maximal;

        }
    }

    return max;
}  

int main(){
    vector<vector<int> > mat={{0,-2,-7,0},{9,2,-6,2},{-4,1,-4,1},{-1,8,0,-2}};
    cout<< MaxSubMatrixSum(mat);
    return 0;
}