Added Cpp code for finding the next palindrome for string inputs

next_palindrome.cpp

@@ -0,0 +1,134 @@
+#include<bits/stdc++.h>
+using namespace std;
+//finding the next palindrome using brute force 
+
+//to make string symmetric
+string mirror(string s){
+    int l=s.length();
+    int j=0;
+    for(int i=l-1;i>=l/2;i--){
+        s[i] =s[j];
+        j++;
+    }
+    return s;
+}
+//to check if middle digits are nine
+int nine(string s){
+    int l=s.length();
+    if(s[l/2]=='9'){
+        return 1;
+    }
+    else{
+        return 0;
+    }
+}
+//if middle digits not nine then increase middle digit by 1
+string inc(string s){
+    int l=s.length();
+    char c=s[l/2];
+    int n= c;
+    n++;
+    char c1=n;
+    if(l%2==0){
+        s[l/2]=c1;
+        s[(l/2)-1]=c1;
+    }
+    else{
+        s[l/2]=c1;
+    }
+    return s;
+}
+//to check if all digit is 9 or not
+int allnine(string s){
+    int l=s.length();
+    int c=0;
+    for(int i=0;i<l;i++){
+        if(s[i]!='9') {
+            c++;
+        }
+    }
+    if(c==0){
+        return 1;
+    }
+    else{
+        return 0;
+    }
+}
+//if all digit are nine then increase by 1
+string ifallnine(string s){
+    int l=s.length();
+    string ns="1";
+    for(int i=0;i<l;i++){
+        ns+="0";
+    }
+    return ns;
+}
+//if middle digit is nine but all digits are not nine:
+//then make middle digit 0 and increase side digits by 1;
+string f(string s){
+    int l=s.length();
+    if(l%2==0){
+        int j=1;
+        for(int i=l/2;i<l;i++){
+            if(s[i]=='9'){
+                s[i]='0';
+                s[l/2-j]='0';
+            }
+            else{
+                int n=s[i];
+                n++;
+                int c=n;
+                s[i]=c;
+                s[l/2-j]=c;
+                break;
+            }
+            j++;
+        }
+    }
+    else{
+        int j=0;
+        for(int i=l/2;i<l;i++){
+        if(s[i]=='9'){
+            s[i]='0';
+            s[l/2-j]='0';
+        }
+        else{
+            int n=s[i];
+            n++;
+            int c=n;
+            s[i]=c;
+            s[l/2-j]=c;
+            break;
+        }
+        j++;
+    }
+    }
+    return s;
+}
+//main function
+int main(){
+    int t;
+    cin>>t;
+    while(t--){
+        string s;
+        cin>>s;
+        string ns=mirror(s);
+        if(ns>s){
+            cout<<ns<<'\n';
+        }
+        else{
+            if(nine(ns)==0){
+                cout<<inc(ns)<<'\n';
+            }
+            else{
+                if(allnine(ns)==1){
+                    cout<<mirror(ifallnine(ns))<<'\n';
+                }
+                else{
+                    cout<<f(ns)<<'\n';
+                }
+            }
+        }
+    }
+    return 0;
+}