// greedy method
string deleteKBits_1(string str,int k){int tlen=str.length();bool flag=true;int len;while(k && flag){len=str.length();for(int i=0;i<len-1;i++){if(str[i]<str[i+1]){str.erase(i,1);flag=true;break;}}k--;}return str.substr(0,tlen-k);
}

// dynamic programming
// time complexity: O(n*k)
// space complexity: O(n*k)
string deleteKBits_2(string str,int k){int tlen=str.length();vector<vector<string> > nums(tlen+1,vector<string>(k+1));string s1,s2;for(int i=1;i<=tlen;i++){for(int j=0;j<i && j<=k;j++){if(j==0){nums[i][j]=str.substr(0,i);}else{s1=nums[i-1][j-1];s2=nums[i-1][j]+str[i-1];if(s1.compare(s2)<=0)nums[i][j]=s2;elsenums[i][j]=s1;}}}return nums[tlen][k];
}// dynamic programming
// time complexity: O(n*k)
// space complexity: O(k)
string deleteKBits_3(string str,int k){int tlen=str.length();vector<string> nums(k+1);string s1,s2,last;for(int i=1;i<=tlen;i++){for(int j=0;j<i && j<=k;j++){if(j==0){last=nums[j];nums[j]=str.substr(0,i);}else{// s1=lasts1=nums[j-1];s2=nums[j]+str[i-1];if(s1.compare(s2)<=0){last=nums[j];nums[j]=s2;}else{last=nums[j];nums[j]=s1;}}}}return nums[k];
}// dynamic programming
// time complexity: O(n*k)
// space complexity: O(k)
string deleteKBits_4(string str,int k){int tlen=str.length();vector<string> nums(k+1);string tmp,s2,last;for(int i=1;i<=tlen;i++){for(int j=0;j<i && j<=k;j++){if(j==0){last=nums[j];nums[j]=str.substr(0,i);}else{// s1=last// s1=nums[j-1];s2=nums[j]+str[i-1];if(last.compare(s2)<=0){last=nums[j];nums[j]=s2;}else{tmp=nums[j];nums[j]=last;last=tmp;}}}}return nums[k];
}

int main()
{string str="2319274";int k=3;cout <<deleteKBits_1(str,k)<< endl;cout <<deleteKBits_2(str,k)<< endl;cout <<deleteKBits_3(str,k)<< endl;cout <<deleteKBits_4(str,k)<< endl;return 0;
}