49_jianzhi_firstDup.cpp

class Solution {
public:
    // Parameters:
    //        numbers:     an array of integers
    //        length:      the length of array numbers
    //        duplication: (Output) the duplicated number in the array number
    // Return value:       true if the input is valid, and there are some duplications in the array number
    //                     otherwise false
    bool duplicate(int numbers[], int length, int* duplication) {
        for(int i = 0; i< length; i++){
            int index = numbers[i];
            if(index >= length)
                index -= length;
            if(numbers[index] >= length){
                numbers[i] -= length;
                duplication[0] = numbers[i];
                return true;
            }
            numbers[index] += length;
        }
        return false;
    }
};