lintcode_189. 丢失的第一个正整数

给出一个无序的整数数组，找出其中没有出现的最小正整数。

样例

如果给出 [1,2,0], return 3
如果给出 [3,4,-1,1], return 2

class Solution:
    """
    @param: A: An array of integers
    @return: An integer
    """
    def firstMissingPositive(self, A):
        # write your code here
        if not A:
            return 1
        A = sorted(A)
        ans = 1
        for i in A:
            if i < ans:
                continue
            if i > ans:
                return ans
            ans += 1
        return ans

九章算法参考：

class Solution:
    # @param A, a list of integers
    # @return an integer
    def firstMissingPositive(self, A):
        # write your code here
        n = len(A)
        i = 0
        if n == 0: 
            return 1
        while i < n:
            while A[i] != i + 1 and A[i] <= n and A[i] > 0 and A[i] != A[A[i] - 1]: 
                t = A[i]
                A[i] = A[A[i] - 1] 
                A[t - 1] = t
            i = i + 1
        for i in xrange(n):
            if A[i] != i + 1: return i + 1
        return n + 1