seven_triple's blog

By seven_triple, history, 5 years ago, In English
#include<bits/stdc++.h>

using namespace std;

string add(string a,string b){
    string c = "";
    a = string(b.length()-a.length(),'0') + a;
    //cout<<"a = "<<a<<"b = "<<b<<"\n";
    int carry = 0;
    for(int i=b.length()-1;i>=0;--i){
        int x = a[i]-'0',y = b[i]-'0';
        int z = x+y+carry;
        c = to_string(z%10) + c;
        carry = z/10;
    }
   if(carry){
       c = to_string(carry) + c;
   }
   return c;
}

int main(){
    vector<int >cache = {1};
    string a = "1",b = "1";
    int index = 2,prev = 1;
    while(cache.size() <= 5000){
        index++;
        string c = add(a,b);
        a = b;
        b = c;
      //  cout<<c<<"\n";

        int curr = c.length();
        if(curr > prev){
            cache.push_back(index);
        }
        prev = curr;
    }
    
    int t;
    cin>>t;
    while(t--){
        int n;
        cin>>n;
        cout<<cache[n-1]<<"\n";
    }
    return 0;
}

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5 years ago, # |
Rev. 2   Vote: I like it +3 Vote: I do not like it

Your code is $$$O(n^3)$$$. For n = 5000 this will be slow. You can speed up this to O(n^2) if you instead of c = to_string(z%10) + c just create c with enough digits and write to it without + operator.

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    5 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    but i think to_string(z%10)+c does not creating any delay in complexity i can replace it with char(z%10 + '0') + c and it take only o(1) time.