feat: add typescript solution to lc problem: No.0043.Multiply Strings (#585)

Author: zhaocchen

solution/0000-0099/0043.Multiply Strings/README.md

@@ -50,6 +50,40 @@
 
 ```
 
+### **TypeScript**
+
+```ts
+function multiply(num1: string, num2: string): string {
+    if ([num1, num2].includes('0')) return '0';
+    const n1 = num1.length, n2 = num2.length;
+    let ans = '';
+    for(let i = 0; i < n1; i++) {
+        let cur1 = parseInt(num1.charAt(n1 - i - 1), 10);
+        let sum = '';
+        for(let j = 0; j < n2; j++) {
+            let cur2 = parseInt(num2.charAt(n2 - j - 1), 10);
+            sum = addString(sum, cur1 * cur2 + ('0'.repeat(j)));
+        }
+        ans = addString(ans, sum + ('0'.repeat(i)));
+    }
+    return ans;
+};
+
+function addString(s1: string, s2: string): string {
+    const n1 = s1.length, n2 = s2.length;
+    let ans = [];
+    let sum = 0;
+    for (let i = 0; i < n1 || i < n2 || sum > 0; i++) {
+        let num1 = s1.charAt(i) ? parseInt(s1.charAt(i), 10) : 0;
+        let num2 = s2.charAt(i) ? parseInt(s2.charAt(i), 10) : 0;
+        sum += (num1 + num2);
+        ans.unshift(sum % 10);
+        sum = Math.floor(sum / 10);
+    }
+    return ans.join('');
+}
+```
+
 ### **...**
 
 ```

solution/0000-0099/0043.Multiply Strings/README_EN.md

@@ -42,6 +42,40 @@
 
 ```
 
+### **TypeScript**
+
+```ts
+function multiply(num1: string, num2: string): string {
+    if ([num1, num2].includes('0')) return '0';
+    const n1 = num1.length, n2 = num2.length;
+    let ans = '';
+    for(let i = 0; i < n1; i++) {
+        let cur1 = parseInt(num1.charAt(n1 - i - 1), 10);
+        let sum = '';
+        for(let j = 0; j < n2; j++) {
+            let cur2 = parseInt(num2.charAt(n2 - j - 1), 10);
+            sum = addString(sum, cur1 * cur2 + ('0'.repeat(j)));
+        }
+        ans = addString(ans, sum + ('0'.repeat(i)));
+    }
+    return ans;
+};
+
+function addString(s1: string, s2: string): string {
+    const n1 = s1.length, n2 = s2.length;
+    let ans = [];
+    let sum = 0;
+    for (let i = 0; i < n1 || i < n2 || sum > 0; i++) {
+        let num1 = s1.charAt(i) ? parseInt(s1.charAt(i), 10) : 0;
+        let num2 = s2.charAt(i) ? parseInt(s2.charAt(i), 10) : 0;
+        sum += (num1 + num2);
+        ans.unshift(sum % 10);
+        sum = Math.floor(sum / 10);
+    }
+    return ans.join('');
+}
+```
+
 ### **...**
 
 ```

solution/0000-0099/0043.Multiply Strings/Solution.ts

@@ -0,0 +1,29 @@
+function multiply(num1: string, num2: string): string {
+    if ([num1, num2].includes('0')) return '0';
+    const n1 = num1.length, n2 = num2.length;
+    let ans = '';
+    for(let i = 0; i < n1; i++) {
+        let cur1 = parseInt(num1.charAt(n1 - i - 1), 10);
+        let sum = '';
+        for(let j = 0; j < n2; j++) {
+            let cur2 = parseInt(num2.charAt(n2 - j - 1), 10);
+            sum = addString(sum, cur1 * cur2 + ('0'.repeat(j)));
+        }
+        ans = addString(ans, sum + ('0'.repeat(i)));
+    }
+    return ans;
+};
+
+function addString(s1: string, s2: string): string {
+    const n1 = s1.length, n2 = s2.length;
+    let ans = [];
+    let sum = 0;
+    for (let i = 0; i < n1 || i < n2 || sum > 0; i++) {
+        let num1 = s1.charAt(i) ? parseInt(s1.charAt(i), 10) : 0;
+        let num2 = s2.charAt(i) ? parseInt(s2.charAt(i), 10) : 0;
+        sum += (num1 + num2);
+        ans.unshift(sum % 10);
+        sum = Math.floor(sum / 10);
+    }
+    return ans.join('');
+}