"Sword refers to offer study" "Face question 52: Build Product Array"

title: Given an array a[0,1,..., n-1], build an array b[0,1,..., n-1], where the elements in B b[i]=a[0]xa[1]x...xa[i-1]xa[i+1]x...xa[n-1], you cannot use division. Thinking of solving problems

For example: a[]={1,2,3} Beg b[]
B[0]=a[1]xa[2]=2x3=6
B[1]=a[0]xa[2]=1x3=3
b[2]=a[0]xa[1]=1x2=2

1.B[0] initialized to 1, starting from subscript I=1, first find out c[i] value and put b[i], that is b[i]=c[i]=c[i-1]xa[i-1], so b[1]=b[1-1]xa[1-1]=b[0]xa[0]=1x1=1,i++

2.b[2]=b[2-1]xa[2-1]=b[1]xa[1]=1x2=2,i++ out of length stop cycle

3.c[i], set a temporary variable temp to initialize to 1

4. From a forward variable array, lengtha=3 initializes the i=lengtha-2=1, ending with a condition of i>=0

5. First loop, temp=tempxa[i+1]=1xa[2]=3, calculates the value of the last element of a in temp,temp equivalent to D[i]

6. Because the previous b[i]=c[i], so let B[i]xd[i] is to save the result, that is b[i]=b[1]=b[1]xtemp=1x3=3,i–=0

7. Calculate B[i]=b[0],temp The value in the previous step is a[2], in this cycle temp=tempxa[0+1]=a[2]xa[1]=3x2=6

8.b[i]=b[0]=b0]xtemp=1x6=6,i–<0 Cycle End

So the b array is {6,3,2}

Code Implementation

Import Java.util.Arrays; Public classTest52 { Public Static Double[]Multiply(Double[] data) {if(Data = =NULL|| Data.length <2) {return NULL; }Double[] result =New Double[Data.length];//result[0] Take 1result[0] =1; for(inti =1; i < data.length; i++) {//First step each result[i] equals to Data[0]*data[1]...data[i-1]            //When i=n-1, the result of this time result[n-1] has been calculated "a"Result[i] = result[i-1] * Data[i-1]; }//tmp save DATA[N-1]*DATA[N-2]...DATA[I+1] Results        DoubleTMP =1;//second step for data[n-1]*data[n-2]...data[i+1]        the results of the//"A" result[n-1] have been calculated, so start operation from Data.length-2         for(inti = data.length-2; I >=0; i--) {tmp *= Data[i +1];        Result[i] *= tmp; }returnResult } Public Static void Main(string[] args) {Double[] Array1 = {1,2,3,4,5}; System. out. println (arrays.tostring (Multiply (array1)));//double expected[] = { -------        Double[] Array2 = {1,2,0,4,5}; System. out. println (arrays.tostring (Multiply (array2)));//double expected[] = {0, 0, 0, 0};        Double[] Array3 = {1,2,0,4,0}; System. out. println (arrays.tostring (Multiply (array3)));//double expected[] = {0, 0, 0, 0, 0};        Double[] Array4 = {1, -2,3, -4,5}; System. out. println (arrays.tostring (Multiply (ARRAY4)));//double expected[] = { -60 , +, -30, +};        Double[] Array5 = {1, -2}; System. out. println (arrays.tostring (Multiply (array5)));//double expected[] = {-2, 1};}}

Run Results

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"Sword refers to offer study" "Face question 52: Build Product Array"