#include <stdio.h>
#include <string.h>
#include <stdlib.h> // atoll
/*
Find the smallest number greater than n using the same digits.
Returns -1 if no such number exists.
Steps:
1. Convert number to array of digits (as chars).
2. Scan from right to left to find the pivot (first digit smaller than the next).
3. If no pivot exists → digits are in descending order → no larger number.
4. Find the smallest digit to the right of pivot that is larger than pivot.
5. Swap them.
6. Reverse the suffix to get the smallest possible number.
*/
long long nextGreaterNumber(long long n) {
char buffer[32];
sprintf(buffer, "%lld", n);
int len = strlen(buffer);
// Step 1: Find pivot
int i;
for (i = len - 2; i >= 0; i--) {
if (buffer[i] < buffer[i + 1]) {
break;
}
}
// No pivot → no larger number
if (i < 0) {
return -1;
}
// Step 2: Find smallest digit greater than pivot to the right
int j;
for (j = len - 1; j > i; j--) {
if (buffer[j] > buffer[i]) {
break;
}
}
// Step 3: Swap pivot with found digit
char temp = buffer[i];
buffer[i] = buffer[j];
buffer[j] = temp;
// Step 4: Reverse the suffix (i+1 to end)
int left = i + 1;
int right = len - 1;
while (left < right) {
char t = buffer[left];
buffer[left] = buffer[right];
buffer[right] = t;
left++;
right--;
}
// Convert back to number
return atoll(buffer);
}
int main() {
printf("Result: %lld\n", nextGreaterNumber(534965)); // 535469
printf("-----------------------------\n");
printf("Result: %lld\n", nextGreaterNumber(111)); // -1 (all digits identical)
printf("-----------------------------\n");
printf("Result: %lld\n", nextGreaterNumber(7600)); // -1 (already the largest)
}
/*
run:
Result: 535469
-----------------------------
Result: -1
-----------------------------
Result: -1
*/
