几个面试经典算法题Java解答

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                                  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;
    }

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