Day1 | 704. 二分查找 | 27. 移除元素 | 977. 有序数组的平方

704. 二分查找 - 力扣（LeetCode）

public class Solution {
    /**
     * @param nums:   The integer array.
     * @param target: Target to find.
     * @return: The first position of target. Position starts from 0.
     */
    public int search(int[] nums, int target) {
        // write your code here
        int left = 0;
        int right = nums.length - 1;
        while (left <= right) {
            int middle = left + (right - left) / 2;
            if (target < nums[middle]) {
                right = middle - 1;
            } else if (target > nums[middle]) {
                left = middle + 1;
            } else {
                if (middle > 0 && nums[middle - 1] == target) {
                    right = middle - 1;
                } else {
                    return middle;
                }
            }
        }
        return -1;
    }
}

27. 移除元素 - 力扣（LeetCode）

class Solution {
    public int removeElement(int[] nums, int val) {
        int idx = 0;
        for (int i = 0; i < nums.length; i++) {
            if (nums[i] != val) {
                nums[idx] = nums[i];
                idx++;
            }
        }
        return idx;
    }
}

977. 有序数组的平方 - 力扣（LeetCode）

class Solution {
    public int[] sortedSquares(int[] nums) {
        int len = nums.length;
        int[] result = new int[len];
        int left = 0, right = len - 1, idx = len - 1;
        while (left <= right) {
            int leftNum = nums[left] * nums[left];
            int rightNum = nums[right] * nums[right];
            if (leftNum <= rightNum) {
                result[idx--] = rightNum;
                right--;
            } else {
                result[idx--] = leftNum;
                left++;
            }
        }
        return result;
    }
}

总结

今天刷题刷了2.5h吧，是有点慢的。 在数组类题目中，我意识到要充分用好指针。