二分法查找

 1 var arr = [1, 2, 3, 4, 5, 6, 7, 8];
 2 var a = 1;
 3 var start = 0;
 4 var end = arr.length - 1;
 5 
 6 // 二分法递归方法
 7 function find(arr, a, start, end) {
 8     var temp = Math.ceil((end + start) / 2);
 9     if (start > end) {
10         console.log('找不到');
11         return false;
12     }
13     if (arr[temp] == a) {
14         console.log("找到了");
15         return true;
16     } else if (arr[temp] > a) {
17         end = temp - 1;
18         find(arr, a, start, end);
19     }
20     else if (arr[temp] < a) {
21         start = temp + 1;
22         find(arr, a, start, end);
23     }
24 }
25 
26 // 二分法非递归
27 function find2(arr, a, start, end) {
28     while ((end - start) >= 0) {
29         var temp = Math.floor((end + start) / 2);
30         console.log(temp)
31         if (arr[temp] == a) {
32             console.log('找到了');
33             return true;
34         } else if (arr[temp] > a) {
35             end = temp - 1;
36         } else if (arr[temp] < a) {
37             start = temp + 1;
38         }
39     }
40     console.log('找不到');
41     return;
42 }
43 
44 find(arr, a, start, end);
45 find2(arr, a, start, end);