feat: update js solution to lc problem: No.0017

Author: rain84

solution/0000-0099/0017.Letter Combinations of a Phone Number/README.md

@@ -462,25 +462,34 @@ impl Solution {
  * @return {string[]}
  */
 var letterCombinations = function (digits) {
-    if (digits.length == 0) {
+    if (digits.length === 0) {
         return [];
     }
     const ans = [];
-    const t = [];
-    const d = ['abc', 'def', 'ghi', 'jkl', 'mno', 'pqrs', 'tuv', 'wxyz'];
-    const dfs = i => {
-        if (i >= digits.length) {
-            ans.push(t.join(''));
+    const n = digits.length;
+    const map = {
+        2: [...'abc'],
+        3: [...'def'],
+        4: [...'ghi'],
+        5: [...'jkl'],
+        6: [...'mno'],
+        7: [...'pqrs'],
+        8: [...'tuv'],
+        9: [...'wxyz'],
+    };
+
+    const dfs = (curr, start) => {
+        if (curr.length === n) {
+            ans.push(curr);
             return;
         }
-        const s = d[parseInt(digits[i]) - 2];
-        for (const c of s) {
-            t.push(c);
-            dfs(i + 1);
-            t.pop();
+        for (let i = start; i < n; i++) {
+            for (const ch of map[digits[i]]) {
+                dfs(curr + ch, i + 1);
+            }
         }
     };
-    dfs(0);
+    dfs('', 0);
     return ans;
 };
 ```

solution/0000-0099/0017.Letter Combinations of a Phone Number/README_EN.md

@@ -458,25 +458,34 @@ impl Solution {
  * @return {string[]}
  */
 var letterCombinations = function (digits) {
-    if (digits.length == 0) {
+    if (digits.length === 0) {
         return [];
     }
     const ans = [];
-    const t = [];
-    const d = ['abc', 'def', 'ghi', 'jkl', 'mno', 'pqrs', 'tuv', 'wxyz'];
-    const dfs = i => {
-        if (i >= digits.length) {
-            ans.push(t.join(''));
+    const n = digits.length;
+    const map = {
+        2: [...'abc'],
+        3: [...'def'],
+        4: [...'ghi'],
+        5: [...'jkl'],
+        6: [...'mno'],
+        7: [...'pqrs'],
+        8: [...'tuv'],
+        9: [...'wxyz'],
+    };
+
+    const dfs = (curr, start) => {
+        if (curr.length === n) {
+            ans.push(curr);
             return;
         }
-        const s = d[parseInt(digits[i]) - 2];
-        for (const c of s) {
-            t.push(c);
-            dfs(i + 1);
-            t.pop();
+        for (let i = start; i < n; i++) {
+            for (const ch of map[digits[i]]) {
+                dfs(curr + ch, i + 1);
+            }
         }
     };
-    dfs(0);
+    dfs('', 0);
     return ans;
 };
 ```

solution/0000-0099/0017.Letter Combinations of a Phone Number/Solution2.js

@@ -3,24 +3,33 @@
  * @return {string[]}
  */
 var letterCombinations = function (digits) {
-    if (digits.length == 0) {
+    if (digits.length === 0) {
         return [];
     }
     const ans = [];
-    const t = [];
-    const d = ['abc', 'def', 'ghi', 'jkl', 'mno', 'pqrs', 'tuv', 'wxyz'];
-    const dfs = i => {
-        if (i >= digits.length) {
-            ans.push(t.join(''));
+    const n = digits.length;
+    const map = {
+        2: [...'abc'],
+        3: [...'def'],
+        4: [...'ghi'],
+        5: [...'jkl'],
+        6: [...'mno'],
+        7: [...'pqrs'],
+        8: [...'tuv'],
+        9: [...'wxyz'],
+    };
+
+    const dfs = (curr, start) => {
+        if (curr.length === n) {
+            ans.push(curr);
             return;
         }
-        const s = d[parseInt(digits[i]) - 2];
-        for (const c of s) {
-            t.push(c);
-            dfs(i + 1);
-            t.pop();
+        for (let i = start; i < n; i++) {
+            for (const ch of map[digits[i]]) {
+                dfs(curr + ch, i + 1);
+            }
         }
     };
-    dfs(0);
+    dfs('', 0);
     return ans;
 };