1. //一开始想当然的写了两层循环
    2. //每次内循环结束，外循环继续，就会重新执行内循环
    3. function findNumberIn2DArray(arr,target) {
    4.     let m = arr.length
    5.     let n = arr[0].length
    6.     for (let i =n-1;  i >= 0; i--){
    7.         for(let j=0; j<m;j++) {
    8.             if(arr[j,i]>target){
    9.                 break
    10.             }else if(arr[j,i]<target){
    11.                 continue
    12.             }else {
    13.                 return true
    14.             }
    15.         }
    17.     }
    18.     return false
    19. }
    20. // 可以用while 
    21. function findNumberIn2DArray(matrix,target) {
    22.     if(matrix.length ==0 || matrix[0].length ==0){
    23.         return false
    24.     }
    25.     let rows = matrix.length
    26.     let cols = matrix[0].length
    27.     let [m,n] = [0,cols-1] 
    28.     while(m<rows&&n>=0){
    29.         let item = matrix[m,n]
    30.         if(item>target){
    31.             n--
    32.         }else if(item<target){
    33.             m++
    34.         }
    35.         if(item===target){
    36.             return true
    37.         }
    38.     }
    39.     return false
    40. }
    41. //不知道为什么超时，之前提交成功的是下面这个就可以
    42. var findNumberIn2DArray = function(matrix, target) {
    43.     if(matrix.length ==0 || matrix[0].length ==0){
    44.         return false
    45.     }
    46.     let rows = matrix.length
    47.     let cols = matrix[0].length
    48.     let row = 0 
    49.     let col = cols-1
    50.     while(row<rows && col>=0){
    51.         let item = matrix[row][col]
    52.         if(item === target){
    53.             return true
    54.         }
    55.         if( item< target ){
    56.             row++
    57.         }else{
    58.             col--
    59.         }
    60.     }
    61.     return false
    63. };