[LeetCode] Find the Closest Palindrome

564. Find the Closest Palindrome

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 minimized between two integers.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491

class BigInt{
public:
string digits;

//Constructors:
BigInt(unsigned long long n = 0);
BigInt(string &);
BigInt(const char *);
BigInt(BigInt &);

//Helper Functions:
friend void divide_by_2(BigInt &a);
friend bool Null(const BigInt &);
friend int Length(const BigInt &);
int operator[](const int)const;

/* * * * Operator Overloading * * * */

//Direct assignment
BigInt &operator=(const BigInt &);

//Post/Pre - Incrementation
BigInt &operator++();
BigInt operator++(int temp);
BigInt &operator--();
BigInt operator--(int temp);

//Addition and Subtraction
friend BigInt &operator+=(BigInt &, const BigInt &);
friend BigInt operator+(const BigInt &, const BigInt &);
friend BigInt operator-(const BigInt &, const BigInt &);
friend BigInt &operator-=(BigInt &, const BigInt &);

//Comparison operators
friend bool operator==(const BigInt &, const BigInt &);
friend bool operator!=(const BigInt &, const BigInt &);

friend bool operator>(const BigInt &, const BigInt &);
friend bool operator>=(const BigInt &, const BigInt &);
friend bool operator<(const BigInt &, const BigInt &);
friend bool operator<=(const BigInt &, const BigInt &);

//Multiplication and Division
friend BigInt &operator*=(BigInt &, const BigInt &);
friend BigInt operator*(const BigInt &, const BigInt &);
friend BigInt &operator/=(BigInt &, const BigInt &);
friend BigInt operator/(const BigInt &, const BigInt &);

//Modulo
friend BigInt operator%(const BigInt &, const BigInt &);
friend BigInt &operator%=(BigInt &, const BigInt &);

//Power Function
friend BigInt &operator^=(BigInt &,const BigInt &);
friend BigInt operator^(BigInt &, const BigInt &);

//Square Root Function
friend BigInt sqrt(BigInt &a);

//Read and Write
friend ostream &operator<<(ostream &,const BigInt &);
friend istream &operator>>(istream &, BigInt &);

//Others
friend BigInt NthCatalan(int n);
friend BigInt NthFibonacci(int n);
friend BigInt Factorial(int n);
string toString() {
string res = "";
for (int i = digits.size() - 1; i >= 0;i--)
res += to_string((short)digits[i]);
return res;
}
};

BigInt::BigInt(string & s){
digits = "";
int n = s.size();
for (int i = n - 1; i >= 0;i--){
if(!isdigit(s[i]))
throw("ERROR");
digits.push_back(s[i] - '0');
}
}
BigInt::BigInt(unsigned long long nr){
do{
digits.push_back(nr % 10);
nr /= 10;
} while (nr);
}
BigInt::BigInt(const char *s){
digits = "";
for (int i = strlen(s) - 1; i >= 0;i--)
{
if(!isdigit(s[i]))
throw("ERROR");
digits.push_back(s[i] - '0');
}
}
BigInt::BigInt(BigInt & a){
digits = a.digits;
}

bool Null(const BigInt& a){
if(a.digits.size() == 1 && a.digits[0] == 0)
return true;
return false;
}
int Length(const BigInt & a){
return a.digits.size();
}
int BigInt::operator[](const int index)const{
if(digits.size() <= index || index < 0)
throw("ERROR");
return digits[index];
}
bool operator==(const BigInt &a, const BigInt &b){
return a.digits == b.digits;
}
bool operator!=(const BigInt & a,const BigInt &b){
return !(a == b);
}
bool operator<(const BigInt&a,const BigInt&b){
int n = Length(a), m = Length(b);
if(n != m)
return n < m;
while(n--)
if(a.digits[n] != b.digits[n])
return a.digits[n] < b.digits[n];
return false;
}
bool operator>(const BigInt&a,const BigInt&b){
return b < a;
}
bool operator>=(const BigInt&a,const BigInt&b){
return !(a < b);
}
bool operator<=(const BigInt&a,const BigInt&b){
return !(a > b);
}

BigInt &BigInt::operator=(const BigInt &a){
digits = a.digits;
return *this;
}

BigInt &BigInt::operator++(){
int i, n = digits.size();
for (i = 0; i < n && digits[i] == 9;i++)
digits[i] = 0;
if(i == n)
digits.push_back(1);
else
digits[i]++;
return *this;
}
BigInt BigInt::operator++(int temp){
BigInt aux;
aux = *this;
++(*this);
return aux;
}

BigInt &BigInt::operator--(){
if(digits[0] == 0 && digits.size() == 1)
throw("UNDERFLOW");
int i, n = digits.size();
for (i = 0; digits[i] == 0 && i < n;i++)
digits[i] = 9;
digits[i]--;
if(n > 1 && digits[n - 1] == 0)
digits.pop_back();
return *this;
}
BigInt BigInt::operator--(int temp){
BigInt aux;
aux = *this;
--(*this);
return aux;
}

BigInt &operator+=(BigInt &a,const BigInt& b){
int t = 0, s, i;
int n = Length(a), m = Length(b);
if(m > n)
a.digits.append(m - n, 0);
n = Length(a);
for (i = 0; i < n;i++){
if(i < m)
s = (a.digits[i] + b.digits[i]) + t;
else
s = a.digits[i] + t;
t = s / 10;
a.digits[i] = (s % 10);
}
if(t)
a.digits.push_back(t);
return a;
}
BigInt operator+(const BigInt &a, const BigInt &b){
BigInt temp;
temp = a;
temp += b;
return temp;
}

BigInt &operator-=(BigInt&a,const BigInt &b){
if(a < b)
throw("UNDERFLOW");
int n = Length(a), m = Length(b);
int i, t = 0, s;
for (i = 0; i < n;i++){
if(i < m)
s = a.digits[i] - b.digits[i]+ t;
else
s = a.digits[i]+ t;
if(s < 0)
s += 10,
t = -1;
else
t = 0;
a.digits[i] = s;
}
while(n > 1 && a.digits[n - 1] == 0)
a.digits.pop_back(),
n--;
return a;
}
BigInt operator-(const BigInt& a,const BigInt&b){
BigInt temp;
temp = a;
temp -= b;
return temp;
}

BigInt &operator*=(BigInt &a, const BigInt &b)
{
if(Null(a) || Null(b)){
a = BigInt();
return a;
}
int n = a.digits.size(), m = b.digits.size();
vector<int> v(n + m, 0);
for (int i = 0; i < n;i++)
for (int j = 0; j < m;j++){
v[i + j] += (a.digits[i] ) * (b.digits[j]);
}
n += m;
a.digits.resize(v.size());
for (int s, i = 0, t = 0; i < n; i++)
{
s = t + v[i];
v[i] = s % 10;
t = s / 10;
a.digits[i] = v[i] ;
}
for (int i = n - 1; i >= 1 && !v[i];i--)
a.digits.pop_back();
return a;
}
BigInt operator*(const BigInt&a,const BigInt&b){
BigInt temp;
temp = a;
temp *= b;
return temp;
}

BigInt &operator/=(BigInt& a,const BigInt &b){
if(Null(b))
throw("Arithmetic Error: Division By 0");
if(a < b){
a = BigInt();
return a;
}
if(a == b){
a = BigInt(1);
return a;
}
int i, lgcat = 0, cc;
int n = Length(a), m = Length(b);
vector<int> cat(n, 0);
BigInt t;
for (i = n - 1; t * 10 + a.digits[i] < b;i--){
t *= 10;
t += a.digits[i] ;
}
for (; i >= 0; i--){
t = t * 10 + a.digits[i];
for (cc = 9; cc * b > t;cc--);
t -= cc * b;
cat[lgcat++] = cc;
}
a.digits.resize(cat.size());
for (i = 0; i < lgcat;i++)
a.digits[i] = cat[lgcat - i - 1];
a.digits.resize(lgcat);
return a;
}
BigInt operator/(const BigInt &a,const BigInt &b){
BigInt temp;
temp = a;
temp /= b;
return temp;
}

BigInt &operator%=(BigInt& a,const BigInt &b){
if(Null(b))
throw("Arithmetic Error: Division By 0");
if(a < b){
return a;
}
if(a == b){
a = BigInt();
return a;
}
int i, lgcat = 0, cc;
int n = Length(a), m = Length(b);
vector<int> cat(n, 0);
BigInt t;
for (i = n - 1; t * 10 + a.digits[i] < b;i--){
t *= 10;
t += a.digits[i];
}
for (; i >= 0; i--){
t = t * 10 + a.digits[i];
for (cc = 9; cc * b > t;cc--);
t -= cc * b;
cat[lgcat++] = cc;
}
a = t;
return a;
}
BigInt operator%(const BigInt &a,const BigInt &b){
BigInt temp;
temp = a;
temp %= b;
return temp;
}

BigInt &operator^=(BigInt & a,const BigInt & b){
BigInt Exponent, Base(a);
Exponent = b;
a = 1;
while(!Null(Exponent)){
if(Exponent[0] & 1)
a *= Base;
Base *= Base;
divide_by_2(Exponent);
}
return a;
}
BigInt operator^(BigInt & a,BigInt & b){
BigInt temp(a);
temp ^= b;
return temp;
}

void divide_by_2(BigInt & a){
int add = 0;
for (int i = a.digits.size() - 1; i >= 0;i--){
int digit = (a.digits[i] >> 1) + add;
add = ((a.digits[i] & 1) * 5);
a.digits[i] = digit;
}
while(a.digits.size() > 1 && !a.digits.back())
a.digits.pop_back();
}

BigInt sqrt(BigInt & a){
BigInt left(1), right(a), v(1), mid, prod;
divide_by_2(right);
while(left <= right){
mid += left;
mid += right;
divide_by_2(mid);
prod = (mid * mid);
if(prod <= a){
v = mid;
++mid;
left = mid;
}
else{
--mid;
right = mid;
}
mid = BigInt();
}
return v;
}

BigInt NthCatalan(int n){
BigInt a(1),b;
for (int i = 2; i <= n;i++)
a *= i;
b = a;
for (int i = n + 1; i <= 2 * n;i++)
b *= i;
a *= a;
a *= (n + 1);
b /= a;
return b;
}

BigInt NthFibonacci(int n){
BigInt a(1), b(1), c;
if(!n)
return c;
n--;
while(n--){
c = a + b;
b = a;
a = c;
}
return b;
}

BigInt Factorial(int n){
BigInt f(1);
for (int i = 2; i <= n;i++)
f *= i;
return f;
}

istream &operator>>(istream &in,BigInt&a){
string s;
in >> s;
int n = s.size();
for (int i = n - 1; i >= 0;i--){
if(!isdigit(s[i]))
throw("INVALID NUMBER");
a.digits[n - i - 1] = s[i];
}
return in;
}

ostream &operator<<(ostream &out,const BigInt &a){
for (int i = a.digits.size() - 1; i >= 0;i--)
cout << (short)a.digits[i];
return cout;
}

class Solution {
public:
string nearestPalindromic(string n) {
if(n.length() < 2) return to_string(stoll(n)-1);
BigInt val = BigInt(n);
long long half = stoll(n.substr(0,n.length()/2));
BigInt res(1e18), diff(n);
BigInt zero(0ull);
auto check = [&](string x) {
for(int i = 0, j = x.length() - 1; i < j; i++,j--) {
if(x[i] != x[j]) return false;
}
BigInt X = BigInt(x);
BigInt d = val > X ? val - X : X - val;
if(d != zero) {
if(d < diff or (d == diff and X < res)) {
res = X;
diff = d;
return true;
}
}
return false;
};
auto udt = [&](string x) {
if(check(x)) {
BigInt now(x);
BigInt nxt = 2 * val - now;
check(nxt.toString());
}
};
for(long long i = max(1ll,half - 1000); i <= half + 1000; i++) {
string s = to_string(i);
string rev = s;
reverse(begin(rev), end(rev));
if(i < 10) udt(s);
udt(s + rev);
for(int j = 0; j < 10; j++) {
string now = s;
now.push_back(j + '0');
now += rev;
udt(now);
}
}
return res.toString();
}
};



Author: Song Hayoung
Link: https://songhayoung.github.io/2024/02/03/PS/LeetCode/find-the-closest-palindrome/
Copyright Notice: All articles in this blog are licensed under CC BY-NC-SA 4.0 unless stating additionally.