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// 564. Find the Closest Palindrome
#include "leetcode.h"
/*
* given a string 'n' representing an integer, return the closest integer (not
* including itself), which is a palindrome. if there is a tie, return the
* smaller one. the closest is defined as the absolute difference minimised
* between two integers.
*/
static inline void substr(char *str, char *sub, int start, int size) {
memcpy(sub, &str[start], size);
sub[size] = '\0';
}
static long get_palindrome(long prefix, bool even_size) {
long long res = prefix;
if (!even_size)
prefix /= 10;
while (prefix) {
res = res * 10 + prefix % 10;
prefix /= 10;
}
return res;
}
char *nearestPalindromic(char *n) {
int len = strlen(n);
if (len == 1) {
n[0] = (((n[0] - '0') - 1) + '0');
return n;
}
char *ans = (char *)malloc((len + 3) * sizeof(char));
bool even_size = len % 2 ? false : true;
int prefix_size = even_size ? len / 2 - 1 : len / 2;
char *prefix_sub = (char *)malloc((prefix_size + 2) * sizeof(char));
substr(n, prefix_sub, 0, prefix_size + 1);
char *n_end;
long long prefix = strtoll(prefix_sub, &n_end, 10);
long long combinations[5] = {0};
combinations[0] = get_palindrome(prefix, even_size);
combinations[1] = get_palindrome(prefix - 1, even_size);
combinations[2] = get_palindrome(prefix + 1, even_size);
combinations[3] = (long long)(pow(10, len - 1) - 1);
combinations[4] = (long long)(pow(10, len) + 1);
long long diff = INT64_MAX, res = 0, orig_num = strtol(n, &n_end, 10);
for (int i = 0; i < 5; i++) {
long long curr = orig_num - combinations[i];
curr = abs((int)curr);
if (!curr)
continue;
else if (curr == diff && combinations[i] > res)
continue;
else if (fmin(curr, diff) == curr) {
res = combinations[i];
diff = curr;
}
}
sprintf(ans, "%lld", res);
free(prefix_sub);
return ans;
}
int main() {
char *n1 = "123", *n2 = "1";
printf("%s\n", nearestPalindromic(n1)); // expect: 121
printf("%s\n", nearestPalindromic(n2)); // expect: 0
}
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