[algorithm] finds the number of occurrences greater than n/k in the array

Title:

1. Given an array of integers, print the number of occurrences greater than half. If no such number appears, print the prompt message.

such as: 1,2,1 Output 1. The such number is output No.

2. Given an integer array, give an integer k, print all occurrences greater than n/k, and if there is no such number, print the hint.

Answer:

Both questions can use a hash table to record the number of occurrences of each number, with an additional space complexity of O (N).

Other methods:

1. time complexity is O (N). Additional space complexity is O (1).

 Public Static voidPrinthalfmajor (int[] arr) {        intCand = 0; intTimes = 0;  for(inti = 0; i < arr.length; i++) {            if(Times = = 0) {Cand=Arr[i]; Times++; } Else if(Arr[i] = =cand) { times++; } Else{ times--; }} times= 0;  for(inti = 0; i < arr.length; i++) {            if(Arr[i] = =cand) times++; }        if(Times > ARR.LENGTH/2) {System.out.println (cand); } Else{System.out.println ("No such number."); }    }

At the end of the first for loop, if such a number really exists, then the value of Cand is the value you are seeking. But the value of cand is not necessarily the value that is being asked. So finally, you have to use the For loop to judge.

2. time complexity is O (n*k). Additional space complexity is O (K).

 Public Static voidPrintkmajor (int[] arr,intK) {if(K < 2) {System.out.println ("The value of K is invalid."); return; } HashMap<integer, integer> cands =NewHashmap<integer, integer>();  for(inti = 0; I! = arr.length; i++) {            if(Cands.containskey (Arr[i])) {cands.put (Arr[i], Cands.get (arr[i))+ 1); } Else {                if(cands.size () = = K-1) {allcandsminusone (cands); } Else{cands.put (arr[i],1); } }} HashMap<integer, integer> reals =getreals (arr, cands); BooleanHasprint =false;  for(Entry<integer, integer>Set:cands.entrySet ()) {Integer key=Set.getkey (); if(Reals.get (key) > Arr.length/K) {hasprint=true; System.out.print (Key+ " "); }} System.out.println (Hasprint? "": "No such number."); }     Public Static voidAllcandsminusone (Hashmap<integer, integer>map) {List<Integer> removelist =NewLinkedlist<integer>();  for(Entry<integer, integer>Set:map.entrySet ()) {Integer key=Set.getkey (); Integer value=Set.getvalue (); if(Value = = 1) {Removelist.add (key); } map.put (key, Value-1); }         for(Integer removekey:removelist) {map.remove (RemoveKey); }    }     Public StaticHashmap<integer, Integer> getreals (int[] arr, HashMap<integer, integer>cands) {HashMap<integer, integer> reals =NewHashmap<integer, integer>();  for(inti = 0; I! = arr.length; i++) {            intCurnum =Arr[i]; if(Cands.containskey (curnum)) {if(Reals.containskey (curnum)) {reals.put (Curnum, Reals.get (curnum)+ 1); } Else{reals.put (Curnum,1); }            }        }        returnreals; }

[algorithm] finds the number of occurrences greater than n/k in the array