题解 2A

传送门

• 对于前导零的判断：0也可以有前导零，即000也算出现了前导零

大模拟，不过长度为30的话许多人写的会爆long long，懒得卡了

Code:

#include <bits/stdc++.h>
using namespace std;
#define INF 0x3f3f3f3f
#define N 100010
#define ll long long
#define reg register int
//#define int long long 

int n;
char s[100];
int sta[100];

bool check() {
	char* t=s;
	int tem, len;
	bool pre_zero;
	for (int i=1; i<=3; ++i,++t) {
		if (!isdigit(*t)) return 0;
		tem=0, len=0;
		if (*t=='0') pre_zero=1;
		else pre_zero=0;
		while (isdigit(*t)) {
			tem=(tem<<3)+(tem<<1)+((*t)^48);
			if (++len>3) return 0;
			++t;
		}
		if (pre_zero&&len>1) return 0;
		if (tem>255) return 0;
		if (*t!='.') return 0;
	}
	if (!isdigit(*t)) return 0;
	tem=0, len=0;
	if (*t=='0') pre_zero=1;
	else pre_zero=0;
	while (t<s+n && isdigit(*t)) {
		tem=(tem<<3)+(tem<<1)+((*t)^48);
		if (++len>3) return 0;
		++t;
	}
	if (pre_zero&&len>1) return 0;
	if (tem>255) return 0;
	if (t!=s+n) return 0;
	return 1;
}

void read() {
	char* t=s;
	int tem; bool over;
	for (int i=1; i<=4; ++i) {
		tem=0, over=0;
		while (!isdigit(*t)) ++t;
		while (t<s+n && isdigit(*t)) {
			tem=(tem<<3)+(tem<<1)+((*t)^48);
			if (tem>255) over=1;
			++t;
		}
		if (over || tem>255) sta[i]=255;
		else sta[i]=tem;
	}
}

signed main()
{
	freopen("ip.in", "r", stdin);
	freopen("ip.out", "w", stdout);

	scanf("%s", s); n=strlen(s);
	if (check()) puts("YES");
	else {
		puts("NO");
		read();
		printf("%d.%d.%d.%d\n", sta[1], sta[2], sta[3], sta[4]);
	}

	return 0;
}