// 二分查找
main();
function main(){
let arr = [-3,-1,...Array(100).keys()];
let index = run(arr,0);
if(!~index){
console.log("not contain")
}else{
console.log("index:",index,
"\tbefore:",arr[index],
"\tafter:",arr[index+1])
}
}
function run(arr,value){
let end = arr.length - 1;
if(arr === undefined || arr.length === 0
||value<arr[0]||value>arr[end]){
return -1;
}
return half(arr,0,end,value)
}
function half(arr,start,end,value){
if(start+1 >= end) return start;
let mid = start + ((end - start)>>1);
return arr[mid] >= value? half(arr,start,mid,value):half(arr,mid,end,value);
}
