lc704二分查找

思路

注意区间边界，脑中模拟比较情况

代码

class Solution {
    public int search(int[] nums, int target) {
        int low = 0, high = nums.length-1;
        while(low <= high){
            int mid = low + (high-low)/2;
            if (nums[mid] < target){
                low = mid + 1;
            } else if (nums[mid] > target){
                high = mid - 1;
            } else {
                return mid;
            }
        }
        return -1;
    }
}

lc27移除元素

思路

利用双指针用符合条件的后面元素覆盖前面元素

代码

class Solution {
    public int removeElement(int[] nums, int val) {
        int slow = 0, fast = 0;
        while(fast < nums.length){
            if (nums[fast] != val){
                nums[slow] = nums[fast];
                slow++;
                fast++;
            } else {
                fast++;
            }
        }
        return slow;
    }
}

lc977有序数组平方

思路

注意比较正负数平方后的大小

代码

class Solution {
    public int[] sortedSquares(int[] nums) {
        int left = 0, right = nums.length-1, k = nums.length-1;
        int[] newNums = new int[nums.length];
        while (left <= right){
            if (nums[left]*nums[left] > nums[right]*nums[right]){
                newNums[k--] = nums[left]*nums[left++];
            } else {
                newNums[k--] = nums[right]*nums[right--];
            }
        }
        return newNums;
    }
}