feat: 两个大数相加

lib/add.js

@@ -1,5 +1,30 @@
-function add() {
-  // 实现该函数
+  function add(a, b) {
+    // 实现该函数
+    if (typeof a === 'number') a = String(a)
+    if (typeof b === 'number') b = String(b)
+
+    //取两个数字的最大长度
+    const maxLength = Math.max(a.length, b.length)
+
+    //用0去补齐长度
+    a = a.padStart(maxLength, 0)
+    b = b.padStart(maxLength, 0)
+
+    let temp = 0
+    // 进位的标志
+    let carry = 0 
+    let sum = ''
+
+    for(let i = maxLength - 1; i >=0; i--) {
+      temp = parseInt(a[i]) + parseInt(b[i]) + carry
+      carry = Math.floor(temp / 10)
+      sum = temp % 10 + sum
+    }
+
+    if (carry === 1) {
+        sum = '1' + sum
+    }
+    return sum
 }
 
 module.exports = add