//二分法查找 function bsearch(A,x){ let l = 0 ,//查找范围的左边届 r = A.length -1 ,//查找的右边界 guess //猜想位置 while(l<=r){ guess = Math.floor((l+r)/2) if(A[guess] === x )return guess else if(A[guess]>x) r = guess -1 else l = guess+1 //循环不变式，1.新查找范围左，2.新查找范围右 } }