剑指offer题目11-20

面试题11：数值的整数次方

public class Solution {
    public double Power(double base, int exponent) {

        if(exponent == 0)
            return 1.0;
        if(exponent == 1)
            return base;
        double res = Power(base ,exponent/2);

        boolean isNeg = false;
        if(exponent < 0)
            isNeg = true;
        exponent = Math.abs(exponent);

        res = res * res;
        if(exponent % 2 == 1){
            if(isNeg == false){
                res = res * base;
            }else if(isNeg == true){
                res = res * 1/base;
            }           
        }
        return res;
  }
}

面试题14：调整数组顺序使奇数位于偶数前面

public class Solution {
    public void reOrderArray(int [] array) {
        int len = array.length;
        int index = 0;
        for(int i=0;i<array.length;i++){
            int tmp = array[i];
            int j = i-1;
            if((array[i]%2)!=0){
                while(j>=0 && (array[j]%2)==0){
                    array[j+1] = array[j];
                    j--;
                }
                array[j+1] = tmp;
            }
        }
    }
}

面试题15：链表中倒数第k个结点

public class Solution {
    public ListNode FindKthToTail(ListNode head,int k) {        
        if(head == null || k==0) return null;        
        ListNode p1 = head;
        ListNode p2 = head;
        int i = 0;
        while(i<k-1){
            if(p2.next != null){
                p2 = p2.next;
                i++;
            }else{
                return null;
            }
        }
        while(p2.next!=null){
            p1 = p1.next;
            p2 = p2.next;
        }
        return p1;
    }
}

面试题16：反转链表

public class Solution {
    public ListNode ReverseList(ListNode head) {
        if(head == null) return null;
        if(head.next == null) return head;
        ListNode pre = null;
        ListNode p   = head;
        while(p != null){
            ListNode tmp = p.next;
            p.next = pre;
            pre = p;
            p = tmp;
        }
        return pre;
    }
}

面试题17：合并两个排序的链表

public class Solution {
    public ListNode Merge(ListNode list1,ListNode list2) {
        if(list1 == null && list2 == null) return null;
        ListNode newHead = new ListNode(0);
        ListNode p = newHead;
        while(list1 != null && list2 != null){
            if(list1.val <= list2.val){
                p.next = list1;
                p = p.next;
                list1 = list1.next;
            }else{
                p.next = list2;
                p = p.next;
                list2 = list2.next;
            }
        }
        ListNode tmp = (list1==null)?list2:list1;
        while(tmp!=null){
            p.next = tmp;
            p = p.next;
            tmp = tmp.next;
        }
        return newHead.next;
    }
}

面试题18：树的子结构

public class Solution {
    public boolean HasSubtree(TreeNode root1,TreeNode root2) {
        if(root2 == null) return false;
        if(root1 == null) return false;
        return isSub(root1,root2) || isSub(root1.left,root2) || isSub(root1.right,root2);
    }
    public boolean isSub(TreeNode root1,TreeNode root2){
        if(root2 == null) return true;
        if(root1 == null) return false;
        if(root1.val != root2.val){
            return false;
        }else{
            return isSub(root1.left,root2.left) && isSub(root1.right,root2.right);
        }
    }
}

面试题19：二叉树的镜像

public class Solution {
    public void Mirror(TreeNode root) {
        if(root == null) return;
        if(root.left == null && root.right==null) return;
        TreeNode tmp = root.left;
        root.left = root.right;
        root.right = tmp;

        if(root.left != null){
            Mirror(root.left);
        }
        if(root.right != null){
            Mirror(root.right);
        }
    }
}

面试题20：顺时针打印矩阵

import java.util.ArrayList;
public class Solution {
    public ArrayList<Integer> printMatrix(int [][] matrix) {
           ArrayList<Integer> list = new ArrayList<Integer>();
        if(matrix.length == 0) return list;
        int m = matrix.length;
        int n = matrix[0].length;
        int x=0,y=0;
        while(m>0 && n>0){
            if(m==1){
                for(int i=0;i<n;i++){
                    list.add(matrix[x][y++]);
                }
                break;
            }else if(n == 1){
                for(int i=0;i<m;i++){
                    list.add(matrix[x++][y]);
                }
                break;
            }
            for(int i=0;i<n-1;i++){
                list.add(matrix[x][y++]);
            }
            for(int i=0;i<m-1;i++){
                list.add(matrix[x++][y]);
            }
            for(int i=0;i<n-1;i++){
                list.add(matrix[x][y--]);
            }
            for(int i=0;i<m-1;i++){
                list.add(matrix[x--][y]);
            }
            m = m - 2;
            n = n - 2;
            x = x + 1;
            y = y + 1;
        }
        return list;
    }
}

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