First Missing Positive

First Missing Positive

Problem:

Given an unsorted integer array, find the first missing positive integer.

Ideas:

A[a[i] [= A[i] Classic applications

My Code:

 Public classSolution { Public intFirstmissingpositive (int[] nums) {        if(nums==NULL|| nums.length==0)return1; intLen =nums.length; inti = 0;  while(I <Len) {            if(Nums[i] <= 0) {i++; }            Else            {                intindex =Nums[i]; if(Index >Len) {Nums[i]= 0; I++; }                Else                {                    if(Nums[index-1] = = index) i++; Else                    {                        intTMP = Nums[index-1]; Nums[index-1] =Nums[i]; Nums[i]=tmp; }                }            }        }         for(intk=0; k<len; k++)        {            if(Nums[k]! = k+1)returnK+1; }        returnLen+1; }    }

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Others code:

//Solution 2:     Public intFirstmissingpositive (int[] A) {//bug 3:when length is 0, return 1;        if(A = =NULL) {            return0; }         for(inti = 0; i < a.length; i++) {            //1:a[i] is in the range; //2:a[i] > 0. //3:the target is different;             while(A[i] <= a.length && a[i] > 0 && a[a[i]-1]! =A[i]) {Swap (A, I, A[i]-1); }        }                 for(inti = 0; i < a.length; i++) {            if(A[i]! = i + 1) {                returni + 1; }        }                returnA.length + 1; }

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The Learning Place:

• Carefully below this piece of code, each a[i] has a mission, what is called the end of the mission, after the ups and downs of the process A[i] The value of several changes, but a[a[i] [= A[i] succeeded, at this moment the mission is over.

 while (A[i] <= a.length && a[i] > 0 && a[a[i]-1]! = A[i])                {-1);                }

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• Change a bad habit

First Missing Positive