package pointer_to_offer;

import java.util.Random;

/**

* 面试题29：查找数组中出现次数超过一半的数字

* 1. 使用快速排序中的partition方法 和 递归

* 2. 根据题目逻辑，将出现的次数和结果保存起来，由于目标出现次数超过数组的一半，所以遍历结束后结果就是目标

*/

public class MoreThanHalfInArray {

private static Random rand = new Random(47);

public static int findByPartition(int[] data) {

if (data == null) return -1;

int length = data.length;

int middle = length >> 1;

int start = 0;

int end = length - 1;

int index = partition(data, start, end);

while (index != middle) {

if (index > middle) {

end = index - 1;

} else {

start = index + 1;

}

index = partition(data, start, end);

}

int result = data[middle];

//有必要的话再检查一下，这个数字是否真的占据了一半以上(针对非法的输入)

return result;

}

private static int partition(int[] data, int start, int end) {

int index = start + rand.nextInt(end - start);

swap(data, end, index);

int smallPos = start - 1;

for (index = start; index < end; index++) {

if (data[index] < data[end]) {

smallPos++;

swap(data, index, smallPos);

}

}

smallPos++;

swap(data, end, smallPos);

return smallPos;

}

private static void swap(int[] data, int pos1, int pos2) {

if (pos1 == pos2) return;

int temp = data[pos1];

data[pos1] = data[pos2];

data[pos2] = temp;

}

private static int findByLogic(int[] data) {

if (data == null) return -1;

int result = data[0];

int times = 1;

for (int i = 0; i < data.length; i++) {

if (times == 0) {

result = data[i];

times = 1;

} else {

if (result == data[i]) {

times++;

} else {

times--;

}

}

}

return result;

}

public static void main(String[] args) {

int[] data = {1, 2, 3, 4, 1, 1, 1, 1, 1, 1, 3, 5, 1};

System.out.println(findByPartition(data));

System.out.println(findByLogic(data));

}

}

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