File size: 936 Bytes
ae4627d | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 | /*
* Find the first item that occurs an even number of times in an array.
* Remember to handle multiple even-occurrence items and return the first one.
* Return null if there are no even-occurrence items.
*/
/*
* example usage:
* var onlyEven = evenOccurrence([1, 7, 2, 4, 5, 6, 8, 9, 6, 4]);
* console.log(onlyEven); // 4
*/
var evenOccurrence = function(arr) {
var occurrence = {};
var result = [];
for (var i = 0; i < arr.length; i++) {
if( occurrence[ arr[i] ] === undefined ){
occurrence[ arr[i] ] = [i, 1];
// if element already present, increase counter
} else {
occurrence[ arr[i] ][1] += 1;
}
}
var minIdx = Number.POSITIVE_INFINITY;
var tempOcc = null;
for(key in occurrence){
if( occurrence[key][1] % 2 === 0 ){
if( occurrence[key][0] < minIdx ){
minIdx = occurrence[key][0];
tempOcc = parseInt(key);
}
}
}
return tempOcc;
};
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