【丢失的数字(268-java)】

丢失的数字(268-java)

public class LC169_268_missingNumber {
    //异或运算
    public static int missingNumber(int[] nums) {
        int ans = nums.length;
        for (int i = 0; i < nums.length; i++) {
            ans ^= i;
            ans ^= nums[i];
        }
        return ans;
    }

    //hash表
    public int missingNumber22(int[] nums) {
        Set<Integer> set = new HashSet<>();
        int len = nums.length;
        for (int i = 0; i < len; ++i) {
            set.add(nums[i]);
        }
        int i;
        for (i = 0; i <= len; ++i) {
            if (!set.contains(i)) {
                break;
            }
        }
        return i;
    }

    //数学思想
    public int missingNumber66(int[] nums) {
        int sum = 0;
        int len = nums.length;
        for (int num : nums) {
            sum += num;
        }
        return len * (len + 1) / 2 - sum;
    }

    public static void main(String[] args) {
        System.out.println(missingNumber(new int[]{3, 0, 1}));
    }
}