代码随想录day1

704.二分查找：

1.左闭右闭

int search(vector<int>& nums, int target) {
        int right = nums.size() - 1;
        int left = 0;
        while(left < right){
            int middle = left + ((right - left) >> 1);
            if(nums.at(middle) == target){
                return middle;
            }else if(nums[middle] > target){
                right = middle - 1;
            }else{
                left = middle + 1;
            }
        }
        return -1;
        
    }

2.左闭右开

int search(vector<int>& nums, int target) {
        int right = nums.size();
        int left = 0;
        while(left < right){
            int middle = left + ((right - left) >> 1);
            if(nums.at(middle) == target){
                return middle;
            }else if(nums[middle] > target){
                right = middle;
            }else{
                left = middle + 1;
            }
        }
        return -1;
        
    }

遇到问题：

如果middle等变量的类型采用auto，跑测试用例nums=[5] target=-5时会报错index越界，后采用int类型。

27.移除元素

int removeElement(vector<int>& nums, int val) {
        int length = nums.size();
        int count = 0;
        
        for(int i = 0; i < length; i++){
            if(nums[i] == val){
                continue;
            }else{
                nums[count++] = nums[i];
            }
        }
        return count;
    }

977.有序数组的平方

注意：考虑非单调递减数组前后的平方值是最大的，中间的是最小的。遍历时从两头往中间走，从后往前存计算结果，就能达到上述要求

vector<int> sortedSquares(vector<int>& nums) {
        vector<int> result(nums.size());
        int left = 0;
        int right = nums.size() - 1;
        int index = nums.size() - 1;
        while(left <= right){
            int square_left = nums[left] * nums[left];
            int square_right = nums[right] * nums[right];
            if(square_left > square_right){
                result[index--] = square_left;
                left++;
            }else{
                result[index--] = square_right;
                right--;
            }
        }
        return result;
    }