大整数运算
#include <cstdlib>#include <cstdio>#include <vector>#include <map>#include <algorithm>using namespace std;void reverse(char*s) {if (s == NULL ) return;char *e = s + strlen(s) - 1;while (s < e) swap(*s, *e), s++, e--;}char* add(char* a, char* b) {if (a == NULL || b == NULL) return NULL;int la = strlen(a), lb = strlen(b);int lc = max(la, lb) + 2;char*c = new char[lc];c[0] = '\0';reverse(a);reverse(b);int carr = 0;int i = 0, t;while (i < la && i < lb) {t = a[i] - '0' + b[i] - '0' + carr;carr = t / 10;c[i] = (t % 10) + '0';i++;}while (i < la) {t = a[i] - '0' + carr;carr = t / 10;c[i++] = (t % 10) + '0';}while (i < lb) {t = b[i] - '0' + carr;carr = t / 10;c[i++] = (t % 10) + '0';}if (carr != 0) c[i++] = '1';c[i] = '\0';reverse(a);reverse(b);reverse(c);return c;}int cmp(char *a, char *b) {int la = strlen(a), lb = strlen(b);if (la != lb) return la - lb;else {while (*a != '\0' && *a == *b) a++, b++;return *a - *b;}}char* minus(char *a, char *b) {if (a == NULL || b == NULL) return NULL;if (cmp(a, b) < 0) {char *c = minus(b, a);reverse(c);int l = strlen(c);c[l] = '-';c[l+1] = '\0';reverse(c);return c;}int la = strlen(a), lb = strlen(b);int lc = max(la, lb) + 2;char*c = new char[lc];c[0] = '\0';reverse(a);reverse(b);int carr = 0;int i = 0, t;while (i < la && i < lb) {t = a[i] - b[i] + carr;if (t < 0) carr = -1, t += 10;else carr = 0;c[i++] = t + '0';}while (i < la) {t = a[i] + carr - '0';if (t < 0) carr = -1, t += 10;else carr = 0;c[i++] = t + '0';}while (--i > 0 && c[i] == '0') ;c[i+1] = '\0';reverse(a);reverse(b);reverse(c);return c;}int main() {char a[] = "2223";char b[] = "222999";auto res = minus(a, b);return 0;}

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