1 <!DOCTYPE html> 2 <html> 3 <head> 4 <title>2.html</title> 5 <script> 6 function binarySearch(arr, findVal, leftIndex, rightIndex) { 7 //使用二分查找的条件是 arr是有序数组 8 //终止条件1. 找不到 9 if (leftIndex > rightIndex) { 10 document.writeln("找不到"); 11 return; 12 } 13 var midIndex = Math.floor((leftIndex + rightIndex) / 2); 14 var midVal = arr[midIndex]; 15 if (midVal > findVal) { 16 binarySearch(arr, findVal, leftIndex, midIndex - 1); 17 } else if (midVal < findVal) { 18 binarySearch(arr, findVal, midIndex + 1, rightIndex); 19 } else { 20 document.writeln("找到了，下标是" + midIndex); //终止条件2. 找到了 21 return; 22 } 23 } 24 var arr = [ 1, 2, 3, 4, 5, 6 ]; 25 //arr 是有序数组 26 binarySearch(arr, 5, 0, arr.length - 1); 27 </script> 28 </head> 29 <body> 30 </body> 31 </html>
1. 有序数组
2. 两个终止条件（找不到leftIndex>rightIndex）
3. 中值下标像下取整