First Missing Positive
class Solution { public int firstMissingPositive(int[] nums) { for(int i=0;i<nums.length;i++){ int correctPos=nums[i]-1; while(((1<=nums[i])&&(nums[i]<=nums.length))&&nums[i]!=nums[correctPos]) { int t=nums[i]; nums[i]=nums[correctPos]; nums[correctPos]=t; correctPos=nums[i]-1; } } for(int i=0;i<nums.length;i++){ if(i+1!=nums[i]){ return i+1; } } return nums.length+1; } }