add: Multiply Strings

Author: hijiangtao

README.md

@@ -11,6 +11,7 @@ This is the solutions collection of my LeetCode submissions, most of them are pr
 |1|[Two Sum](https://leetcode.com/problems/two-sum/) | [JavaScript](./src/two-sum/res.js)|Easy|
 |2|[Add Two Numbers](https://leetcode.com/problems/add-two-numbers/) | [JavaScript](./src/add-two-numbers/res.js)|Medium|
 |3|[Longest Substring Without Repeating Characters](https://leetcode.com/problems/longest-substring-without-repeating-characters/) | [JavaScript](./src/longest-substring-without-repeating-characters/res.js) |Medium|
+|5|[Longest Palindromic Substring](https://leetcode.com/problems/longest-palindromic-substring/) | [JavaScript](./src/longest-palindromic-substring/res.js) |Medium|
 |6|[ZigZag Conversion](https://leetcode.com/problems/zigzag-conversion/) | [JavaScript](./src/zigzag-conversion/res.js) |Medium|
 |7|[Reverse Integer](https://leetcode.com/problems/reverse-integer/) | [JavaScript](./src/reverse-integer/res.js)|Easy|
 |8|[String to Integer (atoi)](https://leetcode.com/problems/string-to-integer-atoi/) | [JavaScript](./src/string-to-integer-atoi/res.js)|Medium|
@@ -25,6 +26,7 @@ This is the solutions collection of my LeetCode submissions, most of them are pr
 |29|[Divide Two Integers](https://leetcode.com/problems/divide-two-integers/) | [JavaScript](./src/divide-two-integers/res.js)|Medium|
 |33|[Search in Rotated Sorted Array](https://leetcode.com/problems/search-in-rotated-sorted-array/) | [JavaScript](./src/search-in-rotated-sorted-array/res.js)|Medium|
 |34|[Search for a Range](https://leetcode.com/problems/search-for-a-range/) | [JavaScript](./src/search-for-a-range/res.js)|Medium|
+|43|[Multiply Strings](https://leetcode.com/problems/multiply-strings/) | [JavaScript](./src/multiply-strings/res.js)|Medium|
 |46|[Permutations](https://leetcode.com/problems/permutations/) | [JavaScript](./src/permutations/res.js)|Medium|
 |48|[Rotate Image](https://leetcode.com/problems/rotate-image/) | [JavaScript](./src/rotate-image/res.js)|Medium|
 |54|[Spiral Matrix](https://leetcode.com/problems/spiral-matrix/) | [JavaScript](./src/spiral-matrix/res.js)|Medium|

src/longest-palindromic-substring/res.js

@@ -0,0 +1,44 @@
+/**
+ * res.js
+ * @authors Joe Jiang (hijiangtao@gmail.com)
+ * @date    2017-05-10 17:35:02
+ * 
+ * @param {string} s
+ * @return {string}
+ */
+let longestPalindrome = function(s) {
+   let len = s.length,
+        end = len-1,
+        sarray = s.split('');
+        
+    if(len<2) {
+        return s;
+    }
+    
+    let resfrom = 0, 
+        resto = 0;
+    for(let i=0; i<end; i++) {
+        expandPalindrome(i,i);
+        if (sarray[i] === sarray[i+1]) {
+            expandPalindrome(i,i+1);
+        }
+    }
+    
+    return s.substring(resfrom, resto+1);
+    
+    function expandPalindrome(start, stop) {
+        while (start>0 && stop<end) {
+            if (sarray[start-1] === sarray[stop+1]) {
+                start--;
+                stop++;
+            } else {
+                break;
+            }
+        }
+        
+        if (stop-start>resto-resfrom) {
+            resfrom = start;
+            resto = stop;
+        }
+    }
+};

src/multiply-strings/res.js

@@ -0,0 +1,66 @@
+/**
+ * res.js
+ * @authors Joe Jiang (hijiangtao@gmail.com)
+ * @date    2017-05-10 18:08:05
+ * 
+ * @param {string} num1
+ * @param {string} num2
+ * @return {string}
+ */
+
+let multiply = function(num1, num2) {
+    let len1 = num1.length,
+        len2 = num2.length,
+        maxlen = len1 > len2 ? len1 : len2,
+        res = [0],
+        base = num1.split('').map(e => Number.parseInt(e)),
+        shift = 0;
+
+    // console.log(base);
+    for (let i = len2 - 1; i >= 0; i--) {
+        let tmp = [], // 存储相乘和数组,倒序 
+            carrybit = 0,
+            mpler = Number.parseInt(num2.charAt(i));
+
+        if (mpler === 0) {
+            shift++;
+            continue;
+        }
+        for (let j = len1 - 1; j >= 0; j--) {
+            let prd = base[j] * mpler + carrybit;
+            carrybit = Math.floor(prd / 10);
+            tmp.push(prd % 10);
+        }
+        if (carrybit) tmp.push(carrybit);
+        let tmplen = tmp.length + shift;
+        // 补0操作
+        for (let j = tmplen - res.length; j > 0; j--) {
+            res.push(0);
+        }
+
+        // 相加操作
+        tmplen = tmp.length;
+        carrybit = 0;
+        for (let j = 0; j < tmplen; j++) {
+            // console.log(res[j+shift], tmp[j], carrybit);
+            let current = res[j + shift] + tmp[j] + carrybit;
+            res[j + shift] = current % 10;
+            // console.log(current);
+            if (current > 9) {
+                carrybit = 1;
+            } else {
+                carrybit = 0;
+            }
+        }
+        if (carrybit) res.push(1);
+
+        // console.log(res, carrybit);
+        shift++;
+    }
+
+    while (res[res.length - 1] === 0 && res.length > 1) {
+        res.pop();
+    }
+
+    return res.reverse().join('');
+};

src/zigzag-conversion/res.js

@@ -4,7 +4,7 @@
  * @date    2017-05-10 16:32:48
  * 
  * Definition of Zigzag: https://en.wikipedia.org/wiki/Zigzag
- * 
+ * 本题的另一种解法: 每行元素之间下标大小相隔 2n-2, n=numRows
  * @param {string} s
  * @param {number} numRows
  * @return {string}