Problem 4

A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.

Find the largest palindrome made from the product of two 3-digit numbers.

C++:

#include 
     
      using namespace std;const int FROM = 100;const int TO = 999;bool ispalindrome(int product){    int miror = 0, temp;    temp = product;    while(temp) {        miror *= 10;        miror += temp % 10;        temp /= 10;    }    return miror == product;}int main(){    int maxpalindrome = 0, temp;    for(int i=TO; i>=FROM; i--)        for(int j=TO; j>=FROM; j--) {            temp = i * j;            if(temp < maxpalindrome)                break;            if(ispalindrome(temp))                if(temp > maxpalindrome)                    maxpalindrome = temp;        }    cout << maxpalindrome << endl;    return 0;}
     

C++:

#include 
     
      #include 
      
       #include 
       
        #include 
        
         using namespace std;const int MAXN = 1000000;const int FROM = 100;const int TO = 999;struct node {    int a, b, product;    bool operator < (const node& n) const {        return product < n.product;    }};bool ispalindrome1(int product){    char s[MAXN+1];    int start, end;    bool isp = true;    sprintf(s, "%d", product);    start = 0;    end = strlen(s)-1;    while(start <= end) {        if(s[start] != s[end]) {            isp = false;            break;        }        start++;        end--;    }    return isp;}bool ispalindrome2(int product){    int miror = 0, temp;    temp = product;    while(temp) {        miror *= 10;        miror += temp % 10;        temp /= 10;    }    return miror == product;}int main(){    priority_queue
         
           q;    node t;    for(int i=FROM; i<=TO; i++)        for(int j=FROM; j<=TO; j++) {            t.a = i;            t.b = j;            t.product = i * j;            q.push(t);        }    while(!q.empty()) {        t = q.top();        q.pop();        if(ispalindrome2(t.product)) {            cout << t.product << endl;            break;        }    }    return 0;}
         
        
       
      
     

Run results:

906609