Lintcode Medium title: First Missing Positive missing a positive integer

Topic

the first positive integer missing

Give an unordered array of integers to find the smallest positive integers that do not appear.

Sample Example

If given [1,2,0] , return 3 if given [3,4,-1,1] , return2

challenges

Only the time-complexity O (n) algorithm is allowed, and only constant-level space can be used.

Solving

The feeling seems to be very complicated, passing rate of 21% is also relatively low.

Found a bad way to do it.

Steps:

1. First find the minimum value of an integer in the array, min

2. If min>1 is clearly the smallest positive integer in the array is 1

3. Here are the cases where min = = 1 is the minimum value

For this case, it is only necessary to determine whether the smallest I, min + i is in the positive integer part of the array, where a ArrayList is required to store the number of positive integer parts, so that it is convenient to determine whether Min+i is in ArrayList. The min+i of the smallest i is the answer.

Here time complexity and space complexity are both O (N)

 Public classSolution {/**         * @parama:an array of integers *@return: An integer*/     Public intFirstmissingpositive (int[] A) {//Write your code here        if(A.length ==0)            return1; //if (a.length ==1) {//if (a[0]<= 0)//return 1; //return a[0]+1; // }        //1. Find the minimum value for positive numbers//2. Minimum value >1 return 1//3. Minimum value <0 return 1//4. The minimum value is 1, the minimum value up plus 1 does not exist is the answer        intMin =Integer.max_value; intMinint =Integer.max_value; ArrayList<Integer> list =NewArraylist<integer>();  for(inti=0;i< a.length;i++){            if(a[i]>0) {List.add (a[i]); if(A[i] <Min) Min=A[i]; }         }        if(min>1 )            return1; inti = 1; //minimum value equals 1         while(i<=a.length) {            if(!list.contains (Min +i)) {Minint= Min +i;  Break; } I= i + 1; }        returnminint; }}

Java Code

Total time: 2210 Ms

This and looking for the missing number seems very similar, although the rewritten program, understand, but leetcode test sample, resulting in unable to pass

Example: [about] This will get into a dead loop.

The procedure is as follows

 Public classSolution {/**         * @parama:an array of integers *@return: An integer*/     Public intFirstmissingpositive (int[] A) {//Write your code here        if(A.length = = 0)            return1; intn =a.length;  for(intI =0;i< N; i++){             while(A[i]! = i + 1){                if(A[i] <= 0 | | A[i] >N) Break; intTMP =A[i]; A[i]= A[tmp-1]; A[tmp-1] =tmp; }        }         for(intI =0;i< N; i++)            if(A[i]! = i+ 1)                returnI+1; returnn + 1; }}

Java Code

classSolution:#@param A, a list of integers    #@return An integer    deffirstmissingpositive (Self, A):#Write your code here        ifA = =None:return1N=Len (A) Nums=a[:] forIinchrange (n): whileA[i]! = i+1: Nums=a[:]ifA[i]<=0ora[i]>=N: Breaktmp=A[i] A[i]= A[tmp-1] A[tmp-1] =tmp#print ' Before: ', Nums                #print ' later: ', A         forIinchrange (n):ifa[i]!= I +1:                returnI+1returnN +1

Python Code

Lintcode Medium title: First Missing Positive missing a positive integer