## 《程序员代码面试指南》第八章 数组和矩阵问题 在数组中找到出现次数大于N/K 的数

#### 题目

``在数组中找到出现次数大于N/K 的数``

#### java代码

``````package com.lizhouwei.chapter8;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
* @Description: 在数组中找到出现次数大于N/K 的数
* @Author: lizhouwei
* @CreateDate: 2018/5/7 19:58
* @Modify by:
* @ModifyDate:
*/
public class Chapter8_6 {
public void printHalfMajor(int[] arr) {
int cand = 0;
int times = 0;
for (int i = 0; i < arr.length; i++) {
if (times == 0) {
cand = arr[i];
times++;
} else if (cand == arr[i]) {
times++;
} else {
times--;
}
}
times = 0;
for (int i = 0; i < arr.length; i++) {
if (cand == arr[i]) {
times++;
}
}
if (times > arr.length / 2) {
System.out.println("超过一半的元素为：" + cand);
}
}

public void printKMajor(int[] arr, int k) {
Map<Integer, Integer> map = new HashMap<>();
int item = 0;
for (int i = 0; i < arr.length; i++) {
item = arr[i];
if (map.containsKey(item)) {
map.put(item, map.get(item) + 1);
} else if (map.size() ==k - 1) {
allCandMinusOne(map);
} else {
map.put(item, 1);
}
}
Map<Integer, Integer> resultMap = getReals(arr, map);
System.out.print("个数超过" + arr.length / k + "的元素为：");
for (Integer key : resultMap.keySet()) {
if (resultMap.get(key) > arr.length / k) {
System.out.print(key + " ");
}
}

}

public void allCandMinusOne(Map<Integer, Integer> map) {
List<Integer> removeList = new ArrayList<>();
for (Integer key : map.keySet()) {
map.put(key, map.get(key) - 1);
if (map.get(key) == 0) {
}
}
for (Integer key : removeList) {
map.remove(key);
}
}

public Map<Integer, Integer> getReals(int[] arr, Map<Integer, Integer> map) {
Map<Integer, Integer> reals = new HashMap<>();
int item = 0;
for (int i = 0; i < arr.length; i++) {
item = arr[i];
if (map.containsKey(item)) {
if (reals.containsKey(item)) {
reals.put(item, reals.get(item) + 1);
} else {
reals.put(item, 1);
}
}
}
return reals;
}

//测试
public static void main(String[] args) {
Chapter8_6 chapter = new Chapter8_6();
int[] arr = {1, 2, 2, 2, 2, 2, 3, 3};
System.out.print("数组{1, 2,2, 2, 2, 3, 3}中");
chapter.printHalfMajor(arr);
int[] arr1 = {1, 2, 2, 2, 2, 3, 3, 3, 3};
System.out.print("数组{1, 2, 2, 2, 2, 3, 3, 3, 3}中");
chapter.printKMajor(arr1,4);

}
}``````