feat: solve No.273

Author: BaffinLee

201-300/273. Integer to English Words.md

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+# 273. Integer to English Words
+
+- Difficulty: Hard.
+- Related Topics: Math, String, Recursion.
+- Similar Questions: Integer to Roman.
+
+## Problem
+
+Convert a non-negative integer `num` to its English words representation.
+
+ 
+Example 1:
+
+```
+Input: num = 123
+Output: "One Hundred Twenty Three"
+```
+
+Example 2:
+
+```
+Input: num = 12345
+Output: "Twelve Thousand Three Hundred Forty Five"
+```
+
+Example 3:
+
+```
+Input: num = 1234567
+Output: "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"
+```
+
+ 
+**Constraints:**
+
+
+	
+- `0 <= num <= 231 - 1`
+
+
+
+## Solution
+
+```javascript
+/**
+ * @param {number} num
+ * @return {string}
+ */
+var numberToWords = function(num) {
+    if (num === 0) return 'Zero';
+    var words1 = [
+        'One',
+        'Two',
+        'Three',
+        'Four',
+        "Five",
+        "Six",
+        'Seven',
+        'Eight',
+        'Nine',
+    ];
+    var words2 = [
+        'Ten',
+        'Eleven',
+        'Twelve',
+        'Thirteen',
+        'Fourteen',
+        'Fifteen',
+        'Sixteen',
+        'Seventeen',
+        'Eighteen',
+        'Nineteen',
+    ];
+    var words3 = [
+        'Ten',
+        'Twenty',
+        'Thirty',
+        'Forty',
+        'Fifty',
+        'Sixty',
+        'Seventy',
+        'Eighty',
+        'Ninety',
+    ];
+    var getStr = function(number) {
+        var res = [];
+        var num1 = Math.floor(number / 100);
+        if (num1 > 0) {
+            res.push(`${words1[num1 - 1]} Hundred`);
+        }
+        number %= 100;
+        if (number >= 10 && number <= 19) {
+            res.push(words2[number - 10]);
+        } else {
+            var num2 = Math.floor(number / 10);
+            if (num2 > 0) {
+                res.push(words3[num2 - 1]);
+            }
+            number %= 10;
+            if (number > 0) {
+                res.push(words1[number - 1]);
+            }
+        }
+        return res.join(' ');
+    };
+    var res = [];
+    [
+        [Math.pow(10, 9), 'Billion'],
+        [Math.pow(10, 6), 'Million'],
+        [Math.pow(10, 3), 'Thousand'],
+    ].forEach(item => {
+        var num1 = Math.floor(num / item[0]);
+        if (num1 > 0) {
+            res.push(`${getStr(num1)} ${item[1]}`);
+        }
+        num %= item[0];
+    });
+    if (num > 0) {
+        res.push(getStr(num));
+    }
+    return res.join(' ');
+};
+```
+
+**Explain:**
+
+nope.
+
+**Complexity:**
+
+* Time complexity : O(log(n)).
+* Space complexity : O(log(n)).