1. How to use recursion to implement an array summation. int getsum (int *a,int n) {return n==0?0:getsum (a,n-1) +a[n-1];//is mainly written with conditional expressions to be relatively concise}
2. How to print a two-dimensional array with a for loop. for (int i=0;i<m*n;i++) printf ("%d", array[i/n][i%n]);
3. The average number of nodes to move in the sequential table to insert and delete a node. Insertion: Average N/2 Delete: average (n-1)/2
4. How to use recursive algorithm to determine whether an array is incremented. BOOL Isincrease (int a[],int n) {if (n==1) return true; Return (A[n-1]>=a[n-2]) && isincrease (a,n-1); }
5. How to use recursive and non-recursive methods to achieve two-point search.
int binarysearch (int array[],int start,int end,int finddata) { if (start>end) &NBSP ; return-1; int mid= (start+end)/2; if (array[mid]==finddata) { return mid, } &nbs P else if (array[mid]>finddata) { Return binarysearch (Array,start, Mid-1,finddata); else return BinarySearch (Array,mid+1,end,finddata); }//Iteration int binarysearch (int array[],int len,int finddata) { if (Array==null | | len<0) &NBSP ; return-1; int start=0;end=len-1; while (start<=end) { int mid= (start+end)/2;//mid in the loop inside &NB Sp if () ... ELSE if &NBSp end=mid-1;//main change end,start subscript else start=mid+1; }}
6. How to find the number of occurrences of a given number in a sorted array
For example [1,2,2,2,2,3] 2 appears 3 times.
Two-time binary lookups can be done at O (2*logn) time complexity to find the leftmost value Lower, the second find finds the rightmost value Upper, and then count=upper-lower//Iterate int binarysearch (int array [],int len,int FindData, bool isleft) { if (Array==null | | len<0) RETURN-1;&N Bsp int start=0;end=len-1; while (start<=end) { int mid= (start+end)/2;//mid in the loop, middle=l eft + (right-left) >>1); //Prevent overflow, shift is also more efficient. At the same time, each cycle needs to be updated. if (Array[mid=finddata]) { Last=mid; if (isleft)//need to find lower &NB Sp end=mid-1; Other &NBSP ; start=mid+1; &NBSP; ELSE if end=mid-1; else start=mid+1; return last>0?last:-1; }
7. How to calculate the intersection of two ordered arrays. a=0,1,2,3,4 b=1,3,5,7,9
int mixed (int array1[],int n1,int array2[],int n2,int *mixed) {int i=0,j=0,k=0; while (i<n1 && j<n2); if (Array1[i]==array2[j]) {mixed[k++]=array1[i]; i++; j + +; } else if (Array1[i]>array2[j]) {j + +; } else if (Array1[i]<array2[j]) {i++; } return k; }
8. How to find the most repeated number in the array.
C:int Count[max] To record the number of occurrences of each element, where Max is the maximum value for the array C + +: Using the map table #include <map> using namespace std; BOOL Findmostfrequentarray (int *a,int size,int &val) {if (size==0) return false; map< int,int> m; for (int i=0;i<size;i++) {if (+ m[a[i]]>= m[val]) val=a[i]; } return true; }
9. How to find the number of occurrences of more than half of the occurrences in the array in the time complexity of O (n). 2,1,1,2,3,1,1,3 method One, reduce the size: if each deletion of two different put the number (regardless of including the highest frequency words), in the remaining numbers, the highest frequency word is more than 50%, the last remaining must be high-frequency words
int Find (int array[],int len) { int candidate=0; int count=0;   ; for (int i=0;i<len;i++) { if (c ount==0) { / Candidate=array[i]; count=1; } else &NB Sp { if (Candidate==num[i]) count++; Other &NBSP ; count--; &NBSP } } return candidate; }
10. How to find the unique repeating element in the array. Condition restriction: Array A[n], number range in [1,n-1] method: Sum of 1 to n in all arrays
Method 2: The number of distinct or duplicate is a, the remaining N-2 number is different or the result is B, then the n number of different or result is a^a^b. 1 to n-1 the number of different or result for a^b then (a^a^b) ^ (a^b) =a
Method Three: Bitmap method
voidSetbit (
intN) {map[n>>5]=map[n>>5] | (1 << (n&31));//n>>5 is 32 for the whole, n&31 is to seek 32 more}
intTestbit (
intN) {
returnMAP[N>>5] & (1<< (n&31));//determine if the corresponding bit is 1}
intFind
intArray[],
intLen) {
inti,k=0;
for(i=0;i<len;i++) {
if(Testbit (Array[i])) return flase; else Setbit (Array[i]); } return ERROR; }
11. How to determine whether the values in an array are contiguous. 1) 5 number run disorder, such as 8 7 5 0 6 2) 0 can match more than one arbitrary number, 0 can appear multiple times.
12. How to find the elements in the array that appear odd times. Only one element odd number of times, find out to different or extension: n-2 elements appear even several times, two appear odd several times, how to Let in O (1) space complexity, find out these two numbers. 1) Set 2 number for a, B, x=a^b 2) How to ask a? The K-bit in X is 1, then the K-bit of a A/b is necessarily different, all the numbers of K-bits 1 are all XOR, i.e. a. So for (...) if ((a[i]>>k) &1) s=s^a[i]; S is a. 3) How to ask for B? X^a= (a^b) ^a=b
void Find (int a[],int length) {
