Binary Search 有时候我们也把它叫做二进制查找
是一种较为高效的再数组中查找目标元素的方法
我们可以通过递归和非递归两种方式来实现它
//非递归 public static int binarySearch(int[] arr, int x) { int low = 0; int high = arr.length-1; while(low <= high) { int middle = (low + high)/2; if(x == arr[middle]) { return middle; }else if(x <arr[middle]) { high = middle - 1; }else { low = middle + 1; } } return -1; } //递归实现二分查找 public static int binarySearch(int[] dataset,int data,int beginIndex,int endIndex){ int midIndex = (beginIndex+endIndex)/2; if(data <dataset[beginIndex]||data>dataset[endIndex]||beginIndex>endIndex){ return -1; } if(data <dataset[midIndex]){ return binarySearch(dataset,data,beginIndex,midIndex-1); }else if(data>dataset[midIndex]){ return binarySearch(dataset,data,midIndex+1,endIndex); }else { return midIndex; } }
时间复杂度是O(log2 n)的,最差情况是log2(n+1)