MissingInteger

Write a function:
class Solution { public int solution(int[] A); }
that, given a non-empty zero-indexed array A of N integers, returns the minimal positive integer that does not occur in A.
For example, given:
A[0] = 1
A[1] = 3
A[2] = 6
A[3] = 4
A[4] = 1
A[5] = 2
the function should return 5.
Assume that:
N is an integer within the range [1..100,000];
each element of array A is an integer within the range [−2,147,483,648..2,147,483,647].
Complexity:
expected worst-case time complexity is O(N);
expected worst-case space complexity is O(N), beyond input storage (not counting the storage required for input arguments).
Elements of input arrays can be modified.

Solution

class Solution {    public int solution(int[] A) {        // write your code in Java SE 8        int N = A.length;        int[] count = new int[N+2];//[0,N+1]        int curMin = 1;        for(int i = 0; i < A.length; i++){            if(A[i] > N || A[i] < 0) continue;            count[A[i]] = 1;            if(A[i] == curMin){                 while(count[++curMin] != 0);             }        }        return curMin;    }}

点评

对于N个元素的数组，结果的范围在[1, N+1]之间。所以定义了一个A[N+2]数组，其中A[0]没有使用，A[N+1]为了防止count[++curMin]越界。