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

Author: rain84

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

@@ -392,25 +392,34 @@ func letterCombinations(digits string) (ans []string) {
 
 ```ts
 function letterCombinations(digits: string): string[] {
-    if (digits.length == 0) {
+    if (digits.length === 0) {
         return [];
     }
     const ans: string[] = [];
-    const t: string[] = [];
-    const d = ['abc', 'def', 'ghi', 'jkl', 'mno', 'pqrs', 'tuv', 'wxyz'];
-    const dfs = (i: number) => {
-        if (i >= digits.length) {
-            ans.push(t.join(''));
+    const n = digits.length;
+    const map: Record<string, string[]> = {
+        2: [...'abc'],
+        3: [...'def'],
+        4: [...'ghi'],
+        5: [...'jkl'],
+        6: [...'mno'],
+        7: [...'pqrs'],
+        8: [...'tuv'],
+        9: [...'wxyz'],
+    };
+
+    const dfs = (curr: string, start: number) => {
+        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

@@ -388,27 +388,36 @@ func letterCombinations(digits string) (ans []string) {
 
 ```ts
 function letterCombinations(digits: string): string[] {
-    if (digits.length == 0) {
+    if (digits.length === 0) {
         return [];
     }
     const ans: string[] = [];
-    const t: string[] = [];
-    const d = ['abc', 'def', 'ghi', 'jkl', 'mno', 'pqrs', 'tuv', 'wxyz'];
-    const dfs = (i: number) => {
-        if (i >= digits.length) {
-            ans.push(t.join(''));
+    const n = digits.length;
+    const map: Record<string, string[]> = {
+        2: [...'abc'],
+        3: [...'def'],
+        4: [...'ghi'],
+        5: [...'jkl'],
+        6: [...'mno'],
+        7: [...'pqrs'],
+        8: [...'tuv'],
+        9: [...'wxyz'],
+    };
+    const dfs = (curr: string, start: number) => {
+        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;
 }
+
 ```
 
 #### Rust

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

@@ -1,22 +1,31 @@
 function letterCombinations(digits: string): string[] {
-    if (digits.length == 0) {
+    if (digits.length === 0) {
         return [];
     }
     const ans: string[] = [];
-    const t: string[] = [];
-    const d = ['abc', 'def', 'ghi', 'jkl', 'mno', 'pqrs', 'tuv', 'wxyz'];
-    const dfs = (i: number) => {
-        if (i >= digits.length) {
-            ans.push(t.join(''));
+    const n = digits.length;
+    const map: Record<string, string[]> = {
+        2: [...'abc'],
+        3: [...'def'],
+        4: [...'ghi'],
+        5: [...'jkl'],
+        6: [...'mno'],
+        7: [...'pqrs'],
+        8: [...'tuv'],
+        9: [...'wxyz'],
+    };
+
+    const dfs = (curr: string, start: number) => {
+        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;
 }