p41

 

public class  {
    public int firstMissingPositive(int[] nums) {
        int max = 0;
		for (int i = 0; i < nums.length; i++) {
			if (nums[i] > max)
				max = nums[i];
		}
		max = max + 1;
		int[] a = new int[max];
		for (int i = 0; i < nums.length; i++) {
			if (nums[i] > 0)
				a[nums[i]]++;
		}
		for (int i = 1; i < max; i++) {

			if (a[i] == 0)
				return i;
		}
		return max;
    }
}