4747
4848** 方法一:式子变换 + 哈希表**
4949
50- 对于下标对 $(i, j),ドル如果满足条件,那么有 $nums[ i] + rev(nums[ j] ) = nums[ j] + rev(nums[ i] ),ドル即 $nums[ i] - rev(nums[ i] ) = nums[ j] - rev(nums[ j] )$。移项后,有 $nums[ i] - nums[ j] = rev(nums[ j] ) - rev(nums[ i] )$。因此,我们可以将 $nums[ i] - rev(nums[ i] )$ 作为哈希表的键,将 $nums[ i] - nums[ j] $ 作为哈希表的值,统计每个键出现的次数,然后计算每个键对应的值的组合数,最后将所有组合数相加即可。
50+ 对于下标对 $(i, j),ドル如果满足条件,那么有 $nums[ i] + rev(nums[ j] ) = nums[ j] + rev(nums[ i] ),ドル即 $nums[ i] - rev(nums[ i] ) = nums[ j] - rev(nums[ j] )$。移项后,有 $nums[ i] - nums[ j] = rev(nums[ j] ) - rev(nums[ i] )$。
51+ 52+ 因此,我们可以将 $nums[ i] - rev(nums[ i] )$ 作为哈希表的键,统计每个键出现的次数。最后计算每个键对应的值的组合数,相加得到最终的答案。
53+ 54+ 注意答案的取模操作。
5155
5256时间复杂度 $O(n \times \log M),ドル其中 $n$ 和 $M$ 分别是数组 ` nums ` 的长度和数组 ` nums ` 中的最大值。空间复杂度 $O(n)$。
5357
@@ -68,11 +72,28 @@ class Solution:
6872 return y
6973
7074 cnt = Counter(x - rev(x) for x in nums)
75+ mod = 10 ** 9 + 7
76+ return sum (v * (v - 1 ) // 2 for v in cnt.values()) % mod
77+ ```
78+ 79+ ``` python
80+ class Solution :
81+ def countNicePairs (self nums : List[int ]) -> int :
82+ def rev (x ):
83+ y = 0
84+ while x:
85+ y = y * 10 + x % 10
86+ x //= 10
87+ return y
88+ 7189 ans = 0
7290 mod = 10 ** 9 + 7
73- for v in cnt.values():
74- ans = (ans + v * (v - 1 ) // 2 ) % mod
75- return ans
91+ cnt = Counter()
92+ for x in nums:
93+ y = x - rev(x)
94+ ans += cnt[y]
95+ cnt[y] += 1
96+ return ans % mod
7697```
7798
7899### ** Java**
@@ -81,26 +102,48 @@ class Solution:
81102
82103``` java
83104class Solution {
84- private static final int MOD = (int ) 1e9 + 7 ;
85- 86105 public int countNicePairs (int [] nums ) {
87106 Map<Integer , Integer > cnt = new HashMap<> ();
88107 for (int x : nums) {
89108 int y = x - rev(x);
90- cnt. put (y, cnt . getOrDefault(y, 0 ) + 1 );
109+ cnt. merge (y, 1 , Integer :: sum );
91110 }
111+ final int mod = (int ) 1e9 + 7 ;
92112 long ans = 0 ;
93113 for (int v : cnt. values()) {
94- ans = (ans + (long ) v * (v - 1 ) / 2 ) % MOD ;
114+ ans = (ans + (long ) v * (v - 1 ) / 2 ) % mod ;
95115 }
96116 return (int ) ans;
97117 }
98118
99119 private int rev (int x ) {
100120 int y = 0 ;
101- while (x > 0 ) {
121+ for (; x > 0 ; x /= 10 ) {
122+ y = y * 10 + x % 10 ;
123+ }
124+ return y;
125+ }
126+ }
127+ ```
128+ 129+ ``` java
130+ class Solution {
131+ public int countNicePairs (int [] nums ) {
132+ Map<Integer , Integer > cnt = new HashMap<> ();
133+ final int mod = (int ) 1e9 + 7 ;
134+ int ans = 0 ;
135+ for (int x : nums) {
136+ int y = x - rev(x);
137+ ans = (ans + cnt. getOrDefault(y, 0 )) % mod;
138+ cnt. merge(y, 1 , Integer :: sum);
139+ }
140+ return ans;
141+ }
142+ 143+ private int rev (int x ) {
144+ int y = 0 ;
145+ for (; x > 0 ; x /= 10 ) {
102146 y = y * 10 + x % 10 ;
103- x /= 10 ;
104147 }
105148 return y;
106149 }
@@ -112,28 +155,49 @@ class Solution {
112155``` cpp
113156class Solution {
114157public:
115- const int mod = 1e9 + 7;
116- 117158 int countNicePairs(vector<int >& nums) {
159+ auto rev = [ ] (int x) {
160+ int y = 0;
161+ for (; x > 0; x /= 10) {
162+ y = y * 10 + x % 10;
163+ }
164+ return y;
165+ };
118166 unordered_map<int, int> cnt;
119167 for (int& x : nums) {
120168 int y = x - rev(x);
121169 cnt[ y] ++;
122170 }
123171 long long ans = 0;
172+ const int mod = 1e9 + 7;
124173 for (auto& [ _ , v] : cnt) {
125174 ans = (ans + 1ll * v * (v - 1) / 2) % mod;
126175 }
127176 return ans;
128177 }
178+ };
179+ ```
129180
130- int rev(int x) {
131- int y = 0;
132- while (x) {
133- y = y * 10 + x % 10;
134- x /= 10;
181+ ```cpp
182+ class Solution {
183+ public:
184+ int countNicePairs(vector<int>& nums) {
185+ auto rev = [](int x) {
186+ int y = 0;
187+ for (; x > 0; x /= 10) {
188+ y = y * 10 + x % 10;
189+ }
190+ return y;
191+ };
192+ unordered_map<int, int> cnt;
193+ int ans = 0;
194+ const int mod = 1e9 + 7;
195+ for (int& x : nums) {
196+ int y = x - rev(x);
197+ ans = (ans + cnt[y]) % mod;
198+ cnt[y]++;
135199 }
136- return y ;
200+ return ans ;
137201 }
138202};
139203```
@@ -142,11 +206,9 @@ public:
142206
143207``` go
144208func countNicePairs (nums []int ) (ans int ) {
145- const mod int = 1e9 + 7
146209 rev := func (x int ) (y int ) {
147- for x > 0 {
210+ for ; x > 0 ; x /= 10 {
148211 y = y*10 + x%10
149- x /= 10
150212 }
151213 return
152214 }
@@ -155,13 +217,88 @@ func countNicePairs(nums []int) (ans int) {
155217 y := x - rev (x)
156218 cnt[y]++
157219 }
220+ const mod int = 1e9 + 7
158221 for _ , v := range cnt {
159222 ans = (ans + v*(v-1 )/2 ) % mod
160223 }
161224 return
162225}
163226```
164227
228+ ``` go
229+ func countNicePairs (nums []int ) (ans int ) {
230+ rev := func (x int ) (y int ) {
231+ for ; x > 0 ; x /= 10 {
232+ y = y*10 + x%10
233+ }
234+ return
235+ }
236+ cnt := map [int ]int {}
237+ const mod int = 1e9 + 7
238+ for _ , x := range nums {
239+ y := x - rev (x)
240+ ans = (ans + cnt[y]) % mod
241+ cnt[y]++
242+ }
243+ return
244+ }
245+ ```
246+ 247+ ### ** JavaScript**
248+ 249+ ``` js
250+ /**
251+ * @param {number[]} nums
252+ * @return {number}
253+ */
254+ var countNicePairs = function (nums ) {
255+ const rev = x => {
256+ let y = 0 ;
257+ for (; x > 0 ; x = Math .floor (x / 10 )) {
258+ y = y * 10 + (x % 10 );
259+ }
260+ return y;
261+ };
262+ const cnt = new Map ();
263+ for (const x of nums) {
264+ const y = x - rev (x);
265+ cnt .set (y, (cnt .get (y) | 0 ) + 1 );
266+ }
267+ let ans = 0 ;
268+ const mod = 1e9 + 7 ;
269+ for (const [_ , v ] of cnt) {
270+ ans = (ans + Math .floor ((v * (v - 1 )) / 2 )) % mod;
271+ }
272+ return ans;
273+ };
274+ ```
275+ 276+ ``` js
277+ /**
278+ * @param {number[]} nums
279+ * @return {number}
280+ */
281+ var countNicePairs = function (nums ) {
282+ const rev = x => {
283+ let y = 0 ;
284+ for (; x > 0 ; x = Math .floor (x / 10 )) {
285+ y = y * 10 + (x % 10 );
286+ }
287+ return y;
288+ };
289+ let ans = 0 ;
290+ const mod = 1e9 + 7 ;
291+ const cnt = new Map ();
292+ for (const x of nums) {
293+ const y = x - rev (x);
294+ const v = cnt .get (y) | 0 ;
295+ ans = (ans + v) % mod;
296+ cnt .set (y, v + 1 );
297+ }
298+ return ans;
299+ };
300+ ```
301+ 165302### ** ...**
166303
167304```
0 commit comments