1.
package com.example.test;
public class offer01 {
public boolean Find(int target, int[][] array) {
int lines = array.length;
int cols = array[0].length;
int x = 0;
int y = cols - 1;
while (x < lines && y >= 0) {
if (array[x][y] == target)
return true;
if (array[x][y] > target)
y--;
else
x++;
}
return false;
}
}
2.
package com.example.test;
public class offer02 {
// 直接替换
public String replaceSpace(StringBuffer str) {
// return str.toString().replace("", "%20");
// 手动模拟;
StringBuffer result = new StringBuffer();
for (char ch : str.toString().toCharArray()) {
if (ch == ' ')
result.append("%20");
else
result.append(ch);
}
return result.toString();
}
public static void main(String[] args) {
String result = new offer02().replaceSpace(new StringBuffer("we are happy"));
System.out.println(result);
}
}
String:不可变,final声明的字符数组
StringBuilder:可变，不加锁，速度快
StringBuffer:可变，加锁，线程安全，速度慢一点
3.
package com.example.test;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
public class offer03 {
public static void main(String[] args) {
//直接使用Collections的逆序操作函数
ArrayList a = new ArrayList();
a.add(1);
a.add(2);
a.add(3);
a.add(4);
a.add(5);
Collections.reverse(a);
System.out.println(a);
//ArrayList插入，新插入的元素会把之前的往后顶
a=new ArrayList();
a.add(0, 1);
a.add(0, 2);
a.add(0, 3);
a.add(0, 4);
a.add(0, 5);
System.out.println(a);
}
}
ArrayList是list接口的可变数组的实现。查询快，增删慢。
LinkedList是List接口的双向链表的实现。查询慢，增删快
Insert, push the previous one to the back 
Recursive 
4.
public class BuildTree {
public TreeNode reConstructBinaryTree(int [] pre,int [] in) {
TreeNode root=ConstructCore(pre,0,pre.length-1,in,0,in.length-1);
return root;
}
public TreeNode ConstructCore(int[] pre,int startPre,int endPre,int[] in,int startIn,int endIn)
{
if(startPre>endPre||startIn>endIn)
return null;
TreeNode node = new TreeNode(pre[startPre]);
for(int i=startIn;i<=endIn;i++)
{
if(in[i]==pre[startPre])
{
node.left = ConstructCore(pre,startPre+1,startPre+i-startIn,in,startIn,i-1);
node.right =ConstructCore(pre,startPre+i-startIn+1,endPre,in,i+1,endIn);
break;
}
}
return node;
}
}
class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int x) {
val = x; }
}
5. 
6.
7. Fibonacci sequence
recursion
conventional 
optimized storage
8/9. Fibonacci sequence 
10. Fibonacci sequence
11.
public class offer05 {
public static void main(String[] args) {
System.out.println(new offer05().number(10));
}
public int number(int n) {
int ans = 0;
for (int i = 0; i < 32; i++) {
if ((n & 1) == 1)
ans++;
n = n >> 1;
}
return ans;
}
}
12. 
Even bubble sort, odd bubble sort
public class offer06 {
public static void main(String[] args) {
int[] arr = new int[] {
4,3,1,2,2,5};
new offer06().reoder(arr);
System.out.println(Arrays.toString(arr));
}
public void reoder(int[] array) {
for (int i = array.length - 1; i >= 0; i--) {
for (int j = 0; j + 1 <= i; j++) {
if (array[j] % 2 == 0 && array[j + 1] % 2 == 1) {
swap(array, j, j+1);
}
}
}
}
public void swap(int[] array, int i, int j) {
int t = array[j];
array[j] = array[i];
array[i] = t;
}
}
13.
14.
15.
