题解 | #数组中重复的数字#

class Solution {
public:
    int duplicate(vector<int>& numbers) {
        // 类似原地哈希的思想
        // 所有数字都在0到n-1的范围内，这就是可以采用下标来做哈希表的暗示
        int i = 0;
        int n = numbers.size();
        while (i < n) {
            if (numbers[i] < 0 || numbers[i] > n) break;
            if (numbers[i] == i) {
                i++;
                continue;
            } else {
                // 如果 numbers[i] != i，那么numbers[i]理应出现在下标 i = numbers[i]处
                if (numbers[i] == numbers[numbers[i]]) {
                    return numbers[i];
                } else {
                    swap(numbers[i], numbers[numbers[i]]);
                }
            }
        }
        return -1;
    }
};