归并排序

归并排序是分治思想的一种实现。

function mergeSort(arr){
    if(arr.length <= 1) return arr;
    var mid = Math.floor(arr.length/2);
    var leftArr = arr.slice(0, mid);
    var rightArr = arr.slice(mid);
    return merge(mergeSort(leftArr), mergeSort(rightArr));
}
function merge(leftArr, rightArr){
    var result = [];
    while(leftArr.length && rightArr.length){
        if(leftArr[0] < rightArr[0]){
            result.push(leftArr.shift());
        }else{
            result.push(rightArr.shift());
        }
    }
    return result.concat(leftArr, rightArr);
}
console.log('mergeSort', mergeSort([4, 7, 2, 1, 5, 3, 8, 6]));