算法与数据结构（13）—— 二分查找（递归与非递归）

递归

private static int find(Comparable[] arr, int l, int r, Comparable target){
        if(l > r) return -1;

        int mid = (r-l)/2 + l;

        if(arr[mid].compareTo(target) == 0)
            return mid;
        else if(arr[mid].compareTo(target) > 0)
            return find(arr, l, mid-1, target);
        else
            return find(arr, mid+1, r, target);
    }

    public static int find(Comparable[] arr, Comparable target){
        return find(arr, 0, arr.length-1, target);
    }

非递归

public static int find(Comparable[] arr, Comparable target){
        // 在arr[l...r]之中查找target
        int l = 0, r = arr.length - 1;
        while(l <= r){

            int mid = (r - l)/2 + l;

            if(arr[mid].compareTo(target) == 0){
                return mid;
            }else if(arr[mid].compareTo(target) > 0){
                r = mid - 1;
            }else if(arr[mid].compareTo(target) < 0){
                l = mid + 1;
            }
        }

        return -1;
    }