几个面试经典算法题Java解答

Posted 2022-12-12 huangshulang1234

                                  几个面试经典算法题Java解答

题目一：

public class testClockwiseOutput  //顺时针打印一个矩阵  @Test public void test() int[][] num = new int[100][100]; int n = 4; int count =1; for(int i=0;i<n;i++) for(int j =0;j<n;j++)
                num[i][j]=count++;
            
        
        
        output(num,0,n-1);
     public void output(int[][] num,int start,int end) if(start>=end || end<=0)return; for(int i=start;i<=end;i++)
            System.out.println(num[start][i]);
         for(int i=start+1;i<=end;i++)
            System.out.println(num[i][end]);
         for(int i=end-1;i>=start;i--)
            System.out.println(num[end][i]);
         for(int i=end-1;i>start;i--)
            System.out.println(num[i][start]);
        
        output(num,start+1,end-1);
    

题目二：

给出一个排序好的数组和一个数，求数组中连续元素的和等于所给数的子数组

//给出一个排序好的数组和一个数，求数组中连续元素的和等于所给数的子数组  @Test public void test() int[] num = 1,2,2,3,4,5,6,7,8,9; int sum = 7;
        findSum(num,sum);
     public void findSum(int[] num,int sum) int left=0; int right=0; for(int i=0;i<num.length;i++) int curSum = 0;
            left = i;
            right = i; while(curSum<sum)
                curSum += num[right++];
             if(curSum==sum) for(int j=left;j<right;j++)
                    System.out.print(num[j]+" ");
                
                System.out.println();
            
        
    

题目三：

//字符数组组成的所有字符串  @Test public void test() //char[] cs = 'a','b','c','d','e';  char[] cs = 'a','b','c'; int length = cs.length;        
        recursionSwap(cs,0,length);
     public void swap(char[] cs,int index1,int index2) char temp = cs[index1];
        cs[index1]=cs[index2];
        cs[index2]=temp;        
     public void recursionSwap(char[] cs,int start,int length) if(start>=length-1)
            print(cs); return;
         for(int i=start;i<length;i++)
            swap(cs,start,i);
            recursionSwap(cs,start+1,length);    
            swap(cs,start,i);
        
     public void print(char[] cs) for(int i=0;i<cs.length;i++)
            System.out.print(cs[i]);
        
        System.out.println();
    

题目四：

//数组组成的最小数  @Test public void test() int[] num=1,5,9,13,442,44,6,21,211;
        qsort(num,0,num.length-1);
        System.out.println(Arrays.toString(num));
     public void qsort(int[] num,int left,int right) if(left<right) int partition = partition(num,left,right);
            qsort(num,left,partition-1);
            qsort(num,partition+1,right);
            
     public int partition(int[] num,int left,int right) int partition = num[left]; while(left<right) while((num[right]==partition || isMBigerThanN(num,num[right],partition)) && left<right)
                right--;
                        
            swap(num,left,right); while((num[left]==partition || isMBigerThanN(num,partition,num[left])) && left<right)
                left++;
            
            swap(num,left,right);        
         return left;
     public void swap(int[] num,int m,int n) int temp = num[m];
        num[m]=num[n];
        num[n]=temp;
     public boolean isMBigerThanN(int[] num,int m,int n)
        String num1 = String.valueOf(m);
        String num2 = String.valueOf(n); int temp1 = Integer.parseInt(num1+num2); int temp2 = Integer.parseInt(num2+num1); if(temp1>temp2) return true;
         else return false;
        
    

题目五：

//子数组最大和  @Test public void test() int[] num = 1,-2,3,10,-4,7,2,-5; //int[] num = 1,-2,3,10,-4,10,2,-5;  System.out.println(maxSum(num));
     public int maxSum(int[] num) int curSum = 0; int curMaxSum = -99999999; int start = 0; int end = 0; for(int i=0;i<num.length;i++) if(curSum<=0)
                curSum = num[i];
                start = i;
             else
                curSum += num[i];
             if(curSum>curMaxSum)
                curMaxSum = curSum;        
                end = i;
            
         for(int i = start;i<=end;i++)
            System.out.println(num[i]);
         return curMaxSum;
    

题目六：

public class testMinStack  //自定义栈，min函数得到当前最小值  @Test public void test()
        MinStack ms = new MinStack();
        ms.push(5);
        System.out.println(ms.min());
        ms.push(6);
        ms.push(2);
        ms.push(1);
        System.out.println(ms.min());
        ms.pop();
        System.out.println(ms.min());
        ms.pop();
        System.out.println(ms.min());
        
    
 class MinStack private Stack<Integer> minStack = new Stack<Integer>(); private Stack<Integer> stack = new Stack<Integer>(); public int pop()
        minStack.pop(); return stack.pop();
     public void push(int num) if(minStack.size()<=0)
            minStack.push(num); return;
        
        Integer min = minStack.lastElement(); if(num<min)
            minStack.push(num);
         else
            minStack.push(min);
        
        stack.push(num);
     public int min() if(minStack.size()<=0) return -1;
         return minStack.lastElement();
    

题目七：

//找出数组中出现次数大于一半的数  @Test public void test() int[] num = 1,2,2,2,2,2,2,4,2,4,6,4,2,6,8,2,7,7;
        System.out.println(moreThanHaft(num));
     public int moreThanHaft(int[] num) int result = -1; int times = 0; for(int i=0;i<num.length;i++) if(times==0)
                result = num[i];
                times++;
             else if(num[i]==result)
                    times++;
                 else
                    times--;
                
            
         return result;
    

题目八：

//判断一个数组是否是另一个栈的出栈顺序  @Test public void test() int[] num = 1,2,3,4,5; //int[] num1=1,2,3,5,4; int[] num2=2,1,5,3,4;
        Stack<Integer> s1 = new Stack<Integer>();
        Stack<Integer> s2 = new Stack<Integer>(); for(int i=0;i<5;i++)
            s2.push(num2[i]);
        
        
        System.out.println(testOrder(num,s1,s2));
     public boolean testOrder(int[] num,Stack<Integer> s1,Stack<Integer> s2) int length = num.length; for(int i=0;i<length;i++)
            s1.push(num[i]); int s2Num = s2.lastElement(); if(s2Num==s1.lastElement().intValue())
                s1.pop();
                s2.pop();
            
         while(!s1.isEmpty()) if(!s1.pop().equals(s2.pop())) return false;
            
         return true;
    

题目九：

//从扑克牌抽5张牌，0可以为任意数，判断是否是顺子  @Test public void test() int[] num = 0,1,5,3,2;
        System.out.println(check(num));
     public boolean check(int[] num) //0-13 int[] pai = new int[14]; for(int n : num)
            pai[n]+=1;
        
        qsort(num,0,num.length-1); int count = pai[0]; int start = 0; if(num[0]==0)
            start=num[1];
         else
            start=num[0];
         for(int i = start;i<=start+5;i++) if(pai[i]>1)return false;
            count += pai[i];
         if(count == 5)return true; else return false;
        
     public void qsort(int[] num,int left,int right) if(left<right) int partition = partition(num,left,right);
            qsort(num,left,partition-1);
            qsort(num,partition+1,right);
        
     public int partition(int[] num,int left,int right) int partition = num[left]; while(left<right) while(left<right && num[right]>=partition)
                right--;
            
            swap(num,left,right); while(left<right && num[left]<=partition)
                left++;
            
            swap(num,left,right);
         return left;        
     public void swap(int[] num,int m,int n) int temp = num[m];
        num[m]=num[n];
        num[n]=temp;
    

题目十：

//输出第k个丑数(因子只有2，3，5)  @Test public void test()
        findUglyNum(8);
     public void findUglyNum(int index) int[] num = new int[index]; int next = 1;
        num[0]=1; int index2=0; int index3=0; int index5=0; while(next<index) int num2 = num[index2]*2; int num3 = num[index3]*3; int num5 = num[index5]*5;
            
            num[next] = getSuitable(num2,num3,num5); while(num[index2]*2<=num[next])
                index2++;
             while(num[index3]*3<=num[next])
                index3++;
             while(num[index5]*5<=num[next])
                index5++;
                            
            next++;
            
        
        System.out.println(num[index-1]);
     public int getSuitable(int num2,int num3,int num5) int s = num2; if(num3<s)
            s = num3;
         if(num5<s)
            s = num5;
         return s;