diff --git a/com/zerroi/leetcode/ThreeNine/ProductExceptSelf.java b/com/zerroi/leetcode/ThreeNine/ProductExceptSelf.java
new file mode 100644
index 0000000..3123c9a
--- /dev/null
+++ b/com/zerroi/leetcode/ThreeNine/ProductExceptSelf.java
@@ -0,0 +1,35 @@
+package com.zerroi.leetcode.ThreeNine;
+
+public class ProductExceptSelf {
+    public static void main(String[] args) {
+        SolutionFirst solutionFirst = new SolutionFirst();
+        int[] ints = solutionFirst.productExceptSelf(new int[]{1, 2, 3, 4});
+    }
+}
+
+/*
+给你一个整数数组 nums，返回 数组 answer ，其中 answer[i] 等于 nums 中除 nums[i] 之外其余各元素的乘积 。
+
+题目数据 保证 数组 nums之中任意元素的全部前缀元素和后缀的乘积都在  32 位 整数范围内。
+
+请 不要使用除法，且在 O(n) 时间复杂度内完成此题。
+*/
+class SolutionFirst {
+    public int[] productExceptSelf(int[] nums) {
+        int length = nums.length;
+        int[] res = new int[length];
+
+        int temp = 1;
+        for (int i = 0; i < length; i++) {
+            res[i] = temp;
+            temp = temp * nums[i];
+        }
+        int a = 1;
+        for (int i = length - 1; i >= 0; i--) {
+            res[i] = res[i] * a;
+            a = a * nums[i];
+        }
+
+        return res;
+    }
+}
diff --git a/com/zerroi/leetcode/ThreeTen/CanCompleteCircuit.java b/com/zerroi/leetcode/ThreeTen/CanCompleteCircuit.java
new file mode 100644
index 0000000..f57fa01
--- /dev/null
+++ b/com/zerroi/leetcode/ThreeTen/CanCompleteCircuit.java
@@ -0,0 +1,37 @@
+package com.zerroi.leetcode.ThreeTen;
+
+import java.util.Arrays;
+
+public class CanCompleteCircuit {
+    public static void main(String[] args) {
+        SolutionFirst solutionFirst = new SolutionFirst();
+        int res = solutionFirst.canCompleteCircuit(new int[]{2,1,5,3,3,4}, null);
+        System.out.println("res = " + res);
+    }
+}
+/*
+在一条环路上有 n 个加油站，其中第 i 个加油站有汽油 gas[i] 升。
+
+你有一辆油箱容量无限的的汽车，从第 i 个加油站开往第 i+1 个加油站需要消耗汽油 cost[i] 升。你从其中的一个加油站出发，开始时油箱为空。
+
+给定两个整数数组 gas 和 cost ，如果你可以按顺序绕环路行驶一周，则返回出发时加油站的编号，否则返回 -1 。如果存在解，则 保证 它是 唯一 的。
+*/
+class SolutionFirst {
+    public int canCompleteCircuit(int[] gas, int[] cost) {
+        int cur = 0;
+        int station = 0;
+        int stock = 0;
+        for (int i = 0; i < gas.length; i++) {
+            stock += gas[i] - cost[i];
+            cur += gas[i] - cost[i];
+            if (cur < 0) {
+                station = i + 1;
+                cur = 0;
+            }
+        }
+        if (stock < 0) {
+            return -1;
+        }
+        return station;
+    }
+}
diff --git a/com/zerroi/leetcode/ThreeTen/IsPalindrome.java b/com/zerroi/leetcode/ThreeTen/IsPalindrome.java
new file mode 100644
index 0000000..64c0550
--- /dev/null
+++ b/com/zerroi/leetcode/ThreeTen/IsPalindrome.java
@@ -0,0 +1,57 @@
+package com.zerroi.leetcode.ThreeTen;
+
+
+public class IsPalindrome {
+    public static void main(String[] args) {
+        SolutionSecond solutionSecond = new SolutionSecond();
+        solutionSecond.isPalindrome("race a car");
+    }
+}
+
+class SolutionSecond {
+    public boolean isPalindrome(String s) {
+        StringBuilder builder = new StringBuilder();
+        for (int i = 0; i < s.length(); i++) {
+            char c = s.charAt(i);
+            if ((c >= 65 && c <= 90) || (c >= 97 && c <= 122) || (c >= 48 && c <= 59)) {
+                builder.append(String.valueOf(c).toLowerCase());
+            }
+        }
+        String str = builder.toString();
+        return builder.reverse().toString().equals(str);
+    }
+
+    public boolean isPalindromeTow(String s) {
+
+        class Solution {
+            public boolean isPalindrome(String s) {
+                boolean ans = true;
+                int l = 0;
+                int r = s.length() - 1;
+                while (true) {
+                    if (l > r) {
+                        break;
+                    }
+                    char lc = s.charAt(l);
+                    char rc = s.charAt(r);
+                    if (!Character.isLetterOrDigit(lc)) {
+                        l++;
+                        continue;
+                    }
+                    if (!Character.isLetterOrDigit(rc)) {
+                        r--;
+                        continue;
+                    }
+                    if (Character.toLowerCase(lc) == Character.toLowerCase(rc)) {
+                        l++;
+                        r--;
+                    } else {
+                        ans = false;
+                        break;
+                    }
+                }
+                return ans;
+            }
+        }
+    }
+}