34. 在排序数组中查找元素的第一个和最后一个位置

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var searchRange = function(nums, target) {
    let l = -1
    let r = nums.length
    let mid
    while(l+1 != r){
        mid = Math.floor((l+r)/2)
        if(nums[mid] < target){
            l = mid
        }else{
            r = mid
        }
    }
    if(nums[r] != target) return [-1,-1]
    let ans = [r]
    while(nums[r] == target){
        r ++
    }
    ans.push(r-1)
    return ans
};

35. 搜索插入位置

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number}
 */
var searchInsert = function(nums, target) {
    let l =-1
    let r =nums.length
    while(l+1 != r){
        let mid = Math.floor((l+r)/2)
        if(nums[mid]==target) return mid
        else if(nums[mid] < target){
            l=mid
        }else{
            r=mid
        }
    }
    return r
};

69. x 的平方根

/**
 * @param {number} x
 * @return {number}
 */
var mySqrt = function(x) {
    let l = 0
    let r = x + 1
    let mid
    while(l+1 !=r){
        mid = Math.floor((l+r)/2)
        if(mid*mid > x){
            r = mid
        }else{
            l= mid
        }
    }
    return l
};

367. 有效的完全平方数

/**
 * @param {number} num
 * @return {boolean}
 */
var isPerfectSquare = function(num) {
    let l = 0
    let r = num + 1
    let mid
    while(l+1 !=r){
        mid = Math.floor((l+r)/2)
        if(mid*mid > num){
            r = mid
        }else{
            l= mid
        }
    }
    if(l*l < num) return false
    return true

};

26. 删除有序数组中的重复项

/**
 * @param {number[]} nums
 * @return {number}
 */
var removeDuplicates = function(nums) {
    if(nums.length < 2) return nums
    let i = 1
    let target = nums[0]
    for(let j = 1; j < nums.length; j ++){
        if(nums[j] != target){
            nums[i++] = nums[j]
            target =  nums[j]
        }
    }
    return i
};

283. 移动零

/**
 * @param {number[]} nums
 * @return {void} Do not return anything, modify nums in-place instead.
 */
var moveZeroes = function(nums) {
    let i = 0
    let cnt = 0
    for(let j = 0; j < nums.length; j ++){
        if(nums[j] != 0){
            nums[i++] = nums[j]
        }else cnt ++
    }
    
    while(cnt){
        nums[nums.length-cnt] = 0
        cnt --
    }
    
};

844. 比较含退格的字符串

先使用栈来处理一下回退符'#'
然后直接比较就可以了

/**
 * @param {string} s
 * @param {string} t
 * @return {boolean}
 */
var backspaceCompare = function(s, t) {
    let arrs = []
    let arrt = []
    for(let i = 0; i < s.length; i++){
        if(s[i] === '#'){
            if(arrs.length !== 0){
                arrs.pop()
            }
        }else{
            arrs.push(s[i])
        }
    }
    for(let j = 0; j < t.length; j++){
        if(t[j] === '#'){
            if(arrt.length !== 0){
                arrt.pop()
            }
        }else{
            arrt.push(t[j])
        }
    }
    if(arrt.length !== arrs.length) return false
    let index1 = 0
    let index2 = 0
    while(index1 < arrs.length && index2 < arrt.length){
        if(arrs[index1 ++] !== arrt[index2 ++]) return false
    }
    return true
    
};

54. 螺旋矩阵

/**
 * @param {number[][]} matrix
 * @return {number[]}
 */
var spiralOrder = function(matrix) {
    let arr = []
    let m = matrix.length
    let n = matrix[0].length
    for(let i = 0; i < m; i++){
        arr.push((new Array(n)).fill(0))
    }
    let k = 1
    let next = [[0,1],[1,0],[0,-1],[-1,0]]
    let x = 0  
    let y = 0
    let nx = 0
    let ny = 0
    let ans = []
    let flag = 0
    while(k <= m*n){
        x = nx
        y = ny
        arr[x][y] = 1
        ans.push(matrix[x][y])
        nx = x + next[flag][0]
        ny = y + next[flag][1]
        if(nx < 0 || nx >= m || ny < 0 || ny >= n || arr[nx][ny] == 1){
            flag = (flag + 1) % 4
            nx = x + next[flag][0]
            ny = y + next[flag][1]
        }
        k++
    }
    return ans
};