数组有序的情况下：
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
</head>
<body>
<script type="text/javascript">
//顺序必须有序
var num = 100000;
var randomNum = Math.ceil(Math.random()*num);
document.title = randomNum;
var arr = [];
for(var i = 0 ;i<num;i++)
{
arr.push(i)
}
console.log(randomNum);
//======第一种方式=========
function show1(arr,randomNum)
{
console.time(2)
for (var i = 0; i <arr.length; i++) {
if(arr[i] === randomNum)
{
console.timeEnd(2);
return arr[i];
}
}
}
show1(arr,randomNum);
//======第二种方式=========
function show(arr,randomNum)
{
console.time(1)
var first = 0;
var last = arr.length -1;
while(first <= last)
{
var mindex = Math.floor((first + last)/2);
if(randomNum < arr[mindex]) //大于中间值
{
last = mindex -1;
}else if(randomNum > arr[mindex]){
first = mindex +1;
}else{
console.timeEnd(1)
return arr[mindex];
}
}
}
console.log(show(arr,randomNum));
</script>
</body>
</html>
数组无序的情况下：
使用二分 先把数组排列成有序------然后二分 所花的时间比 普通for循环的时间要长
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
</head>
<body>
<script type="text/javascript">
//顺序必须有序
var num = 100000;
var randomNum = Math.ceil(Math.random()*num);
document.title = randomNum;
var arr = [];
for(var i = 0 ;i<num;i++)
{
arr.push(i)
}
//无序的排序
arr.sort(function(){
return Math.random() -0.5;
})
console.log(randomNum);
//======第一种方式=========
function show1(arr,randomNum)
{
console.time(2)
for (var i = 0; i <arr.length; i++) {
if(arr[i] === randomNum)
{
console.timeEnd(2);
return arr[i];
}
}
}
show1(arr,randomNum);
//======第二种方式=========
function show(arr,randomNum)
{
console.time(1)
arr.sort(function(n1,n2){
return n1 -n2;
})
var first = 0;
var last = arr.length -1;
while(first <= last)
{
var mindex = Math.floor((first + last)/2);
if(randomNum < arr[mindex]) //大于中间值
{
last = mindex -1;
}else if(randomNum > arr[mindex]){
first = mindex +1;
}else{
console.timeEnd(1)
return arr[mindex];
}
}
}
console.log(show(arr,randomNum));
</script>
</body>
</html>