class Solution {

    public int firstMissingPositive(int[] nums) {

        int len = nums.length;

        for(int i = 0;i<len;){

            int t = nums[i];

            if(t>0&&t<=len&&t!=nums[t-1])

                swap(nums,i,t-1);

            else

                i++;

        }

        for (int i = 0; i < len; i++) {

           if (i + 1 != nums[i]) {

               return i + 1;

           }

       }

       return len + 1;

    }

     //数组元素交换

     public void swap(int[] nums,int i,int j) {

        int tmp = nums[i];

        nums[i] = nums[j];

        nums[j] = tmp;

     }

}