DuplicationInArray.java

/**
 * Created by Yang on 2017/4/23.
 * 数组中重复的数字：
 *
 * 在一个长度为n的数组里的所有数字都在0到n-1的范围内。 数组中某些数字是重复的，
 * 但不知道有几个数字是重复的。也不知道每个数字重复几次。请找出数组中任意一个重复的数字。
 * 例如，如果输入长度为7的数组{2,3,1,0,2,5,3}，那么对应的输出是重复的数字2或者3。
 */
public class DuplicationInArray {
    // Parameters:
    //    numbers:     an array of integers
    //    length:      the length of array numbers
    //    duplication: (Output) the duplicated number in the array number,length of duplication array is 1,so using duplication[0] = ? in implementation;
    //                  Here duplication like pointor in C/C++, duplication[0] equal *duplication in C/C++
    //    这里要特别注意~返回任意重复的一个，赋值duplication[0]
    // Return value:       true if the input is valid, and there are some duplications in the array number
    //                     otherwise false
    public boolean duplicate(int numbers[],int length,int [] duplication) {
        if(numbers == null || numbers.length < length || length <= 0) {
            return false;
        }

        // 检查是否数字都在[0,n-1]之内
        for (int i = 0; i < length; i++) {
            if(numbers[i] < 0 || numbers[i] >= length) {
                return false;
            }
        }

        for (int i = 0; i < length; i++) {
            while(numbers[i] != i) {
                if(numbers[i] == numbers[numbers[i]]) {
                    duplication[0] = numbers[i];
                    return true;
                }

                // 将numbers[i]放到正确的位置上
                int temp = numbers[i];
                numbers[i] = numbers[temp];
                numbers[temp] = temp;
            }
        }

        return false;
    }

    public static void main(String[] args) {
        DuplicationInArray duplicationInArray = new DuplicationInArray();

        int[] array = new int[]{2,3,1,0,2,5,3};
        int[] duplication = new int[]{0};
        duplicationInArray.duplicate(array, array.length, duplication);
        System.out.println(duplication[0]);
    }
}