From 47e88aac1b881578112d2d6ec43be3d50053a1de Mon Sep 17 00:00:00 2001
From: liu13 <1099976891@qq.com>
Date: Mon, 25 Feb 2019 09:54:51 +0800
Subject: [PATCH] 20190225

---
 code/lc190.java | 25 +++++++++++++++++++++++++
 code/lc191.java | 22 ++++++++++++++++++++++
 code/lc202.java | 32 ++++++++++++++++++++++++++++++++
 code/lc204.java | 23 +++++++++++++++++++++++
 code/lc217.java | 21 +++++++++++++++++++++
 5 files changed, 123 insertions(+)
 create mode 100644 code/lc190.java
 create mode 100644 code/lc191.java
 create mode 100644 code/lc202.java
 create mode 100644 code/lc204.java
 create mode 100644 code/lc217.java

diff --git a/code/lc190.java b/code/lc190.java
new file mode 100644
index 0000000..47bd8a6
--- /dev/null
+++ b/code/lc190.java
@@ -0,0 +1,25 @@
+package code;
+
+/*
+ * 190. Reverse Bits
+ * 题意：转换为二进制，反转，再输出
+ * 难度：Easy
+ * 分类：Bit Manipulation
+ * 思路：做位移操作，自己没想起来，好好看看
+ * Tips：注意 >>> 无符号位移 它不会将所处理的值的最高位视为正负符号，所以作位移处理时，会直接在空出的高位填入0
+ */
+public class lc190 {
+    public static void main(String[] args) {
+        System.out.println(reverseBits(10));
+    }
+    // you need treat n as an unsigned value
+    public static int reverseBits(int n) {
+        int result = 0;
+        for (int i = 0; i < 32 ; i++) {
+            result += n&1;
+            n >>>= 1;       //无视符号右移
+            if(i<31) result<<=1;
+        }
+        return result;
+    }
+}
diff --git a/code/lc191.java b/code/lc191.java
new file mode 100644
index 0000000..13a0ea7
--- /dev/null
+++ b/code/lc191.java
@@ -0,0 +1,22 @@
+package code;
+/*
+ * 191. Number of 1 Bits
+ * 题意：统计二进制数中1的个数
+ * 难度：Easy
+ * 分类：Bit Manipulation
+ * 思路：每次移一位，与运算
+ * Tips：
+ */
+public class lc191 {
+    // you need to treat n as an unsigned value
+    public int hammingWeight(int n) {
+        int sum = 0;
+        int a = 1;
+        while(a!=0){
+            int b = n&a;
+            if(b!=0) sum += 1;
+            a <<= 1;
+        }
+        return sum;
+    }
+}
diff --git a/code/lc202.java b/code/lc202.java
new file mode 100644
index 0000000..6429bd5
--- /dev/null
+++ b/code/lc202.java
@@ -0,0 +1,32 @@
+package code;
+/*
+ * 202. Happy Number
+ * 题意：各位置上的数字循环求平方和，如果可以等于1，则为Happy Number
+ * 难度：Easy
+ * 分类：Hash Table, Math
+ * 思路：如果不会等于1，则会产生循环，用hashset记录之前是否出现过
+ *      也可利用判断链表是否有环的思路，一个计算一步，一个计算两步，看是会相等来判断
+ * Tips：
+ */
+import java.util.HashSet;
+
+public class lc202 {
+    public boolean isHappy(int n) {
+        HashSet hs = new HashSet<Integer>();
+        hs.add(n);
+        int sum = 0;
+        while(true){
+            sum = 0;
+            while(n!=0){
+                sum += Math.pow(n%10,2);
+                n = n/10;
+            }
+            if(sum==1) return true;
+            else if(hs.contains(sum)) break;
+            hs.add(sum);
+            n = sum;
+            System.out.println(sum);
+        }
+        return false;
+    }
+}
diff --git a/code/lc204.java b/code/lc204.java
new file mode 100644
index 0000000..cdf21d3
--- /dev/null
+++ b/code/lc204.java
@@ -0,0 +1,23 @@
+package code;
+/*
+ * 204. Count Primes
+ * 题意：计算小于n的素数的个数
+ * 难度：Easy
+ * 分类：Hash Table, Math
+ * 思路：两个循环，相乘得到的数不是素数。
+ * Tips：
+ */
+public class lc204 {
+    public int countPrimes(int n) {
+        if(n<3) return 0;
+        boolean[] flags = new boolean[n];
+        int sum = 0;
+        for(int i=2; i<n; i++){
+            if(flags[i]==false) sum++;      // 内循环已经计算过了
+            for(int j=2; i*j<n; j++){       // i*j<n
+                flags[i*j] = true;
+            }
+        }
+        return sum;
+    }
+}
diff --git a/code/lc217.java b/code/lc217.java
new file mode 100644
index 0000000..bc6cad4
--- /dev/null
+++ b/code/lc217.java
@@ -0,0 +1,21 @@
+package code;
+
+import java.util.HashSet;
+/*
+ * 217. Contains Duplicate
+ * 题意：数组中是否有重复的数字
+ * 难度：Easy
+ * 分类：Array, Hash Table
+ * 思路：用Hashset记录是否有重复
+ * Tips：
+ */
+public class lc217 {
+    public boolean containsDuplicate(int[] nums) {
+        HashSet hs = new HashSet<Integer>();
+        for(int i=0; i<nums.length; i++){
+            if(hs.contains(nums[i])) return true;
+            hs.add(nums[i]);
+        }
+        return false;
+    }
+}
-- 
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