面试题目集(一)

时间好快

面试题目一：海量无序数据中，得到最小的K个数

考察知识点：大顶堆，堆排序建堆，调整过程

package learning;public class minTopK {/** * 利用大根堆求解无序数组的最小的k个数 */public static void swap(int[] arr,int index1,int index2){int tmp = arr[index1];arr[index1] = arr[index2];arr[index2] = tmp;}public static void heapInsert(int[] arr,int value,int index){arr[index] = value;//index为0的话一定为根节点while(index!=0){int parent = (index -1)/2;if(arr[parent]<arr[index]){swap(arr,parent,index);index = parent;}else{break;}}}public static void heapify(int[] arr,int index,int heapSize){int left = index*2+1;int right = index*2+2;int largest = index;while(left<heapSize){if(arr[left]>arr[index]){largest = left;}if(right<heapSize&&arr[right]>arr[largest]){largest = right;}if(largest!=index){swap(arr,largest,index);}else{break;}index = largest;left = index*2+1;right = index*2+2;}}public static int[] getMinKNumsByHeap(int[] arr,int k){if(k<1||k>arr.length){return arr;}int[] kHeap = new int[k];for(int i=0;i!=k;i++){heapInsert(kHeap,arr[i],i);}for(int i=k;i!=arr.length;i++){if(arr[i]<kHeap[0]){kHeap[0] = arr[i];heapify(kHeap,0,k);}}return kHeap;}public static void main(String[] args) {// TODO Auto-generated method stubint[] arr = {8,4,11,6,7,11,3,9,1};int[] arr_tmp = getMinKNumsByHeap(arr,5);for(int i=0;i<arr_tmp.length;i++){System.out.print(arr_tmp[i]);}}}

面试题目2：给定N个数据，将这N个数据分成两组，使得两组分别求和记作S1,S2，使得|S1-S2|最小，并返回这个绝对差值，比如这N个数为1,2,3,分成两组为A1,A2，A1包含1,2，A2包含3，则返回结果为0

考察知识点：动态规划，背包问题

package qidian;public class Test2 {public static int KnapSack(int num, int weight[], int value[], int x[], int C){        int V[][] = new int[C+1][C+1];        for(int i = 0 ; i <= num-1 ; i++ ){            V[i][0] = 0; //第一列都为0；        }        for(int j = 0 ; j <=C ; j++){            V[0][j]=0;    //第一行都为0        }        for(int i = 1 ; i <= num-1 ; i++){            for(int j = 1 ; j <=C ; j++){                if(j<weight[i])                       V[i][j]=V[i-1][j];                else{                    V[i][j] = Math.max(V[i-1][j], V[i-1][j-weight[i]]+value[i]);                }                           }        }               return 2*C-2*V[num-1][C];             }public static void main(String[] args) { int[] weight = {-1,2,4,4}; //下标都从1开始     int[] value = {-1,2,4,4}; //下标都从1开始     int num = weight.length;     int CAP = 0;for(int k=1;k<num;k++){CAP+=value[k];} CAP = CAP/2;     int[] x = new int[num];    //第0个元素不算，下标都从1开始     int answer = KnapSack(num,weight,value,x,CAP);     System.out.println("answer："+answer);}}

面试题目3：判断一个数是否为回文数

考察知识点：数制

package learning;public class palindrome {/** * 判断一个数是否为回文数 */public static int get_help(int num){int help = 1;while(num/10!=0){num = num/10;help = help*10;}System.out.print(help);return help;}public static boolean ispalindrome(int num){    num = Math.abs(num);int help = get_help(num);while(help>1){int left = num/help;int right = num%10;if(left!=right){return false;}num = num%help/10;help = help/100;}return true;}public static void main(String[] args) {// TODO Auto-generated method stubint a = -1211111;int b = 123321;int c = 2;System.out.print(ispalindrome(a));}}

面试题目4：将无序数组分成四块，不好切割点分别求和，使得和相同

缺点：正负整型符合不能正确求解，有大神可以解决么？

package qidian;import java.util.HashMap;import java.util.Map;public class searchPoints_2 {/** * @param args */    public static void main(String[] args){          //int[] input = {2,0,2,0,2,0,2};     //int[] input = {1,3,1,4,2,2,1,1,2,4};    //int[] input = {2,-1,5,3,-2,-1,4,-3,2,1};    int[] input = {2,0,1,2,0,2,0,2};        int[] sums = new int[input.length];          Map<Integer, Integer> hashMap = new HashMap<Integer, Integer>();            int tmp = 0;          for (int i = 0; i < input.length; ++i) {              tmp += input[i];              sums[i] = tmp;             if(!hashMap.containsKey(tmp)){            hashMap.put(tmp, i);            }                      }            for (int pos1 = 1; pos1 < input.length; ++pos1) {              int sum = sums[pos1] - input[pos1];              if (hashMap.containsKey(sum + sums[pos1])) {                  int pos2 = hashMap.get(sum + sums[pos1]) + 1;                  if (pos2 < input.length && hashMap.containsKey(sum + sums[pos2])) {                      int pos3 = hashMap.get(sum + sums[pos2]) + 1;                      if (pos3 < input.length && sums[sums.length - 1] - sums[pos3] == sum) {                          System.out.println("result:"+pos1 + "---"+pos2+"----"+pos3);                          return;                     }                  }              }          }          return;        }  }