Easy 部分

1. Two Sum

class Solution {
    public int[] twoSum(int[] nums, int target) {
        Map<Integer, Integer> hash = new HashMap<Integer, Integer>();
        int[] res = new int[2];
        for(int i = 0;i < nums.length; ++i){
            if(hash.containsKey(target-nums[i])){
                res[0] = hash.get(target-nums[i]);
                res[1] = i;
                break;
            }
            hash.put(nums[i], i);
        }
        return res;
    }
}

26. Remove Duplicates from Sorted Array

class Solution {
    public int removeDuplicates(int[] nums) {
        int count = 0;
        for(int i = 1; i < nums.length; ++i){
            if(nums[i] != nums[count]){
                nums[++count] = nums[i];
            }
        }
        return count + 1;
    }
}

27. Remove Element

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

由于对顺序没有要求，所以有一种更快的方法

class Solution {
    public int removeElement(int[] nums, int val) {
        int index = 0;
        int len = nums.length;
        while(index < len){
            if(nums[index] == val){
                nums[index] = nums[len - 1];
                --len;
            }else{
                ++index;
            }
        }
        return index;
    }
}

35. Search Insert Position

普通解法

class Solution {
    public int searchInsert(int[] nums, int target) {
        int res = -1;
        for(int i = 0; i < nums.length; ++i){
            if(nums[i] == target || nums[i] > target){
                res = i;
                break;
            }
        }
        if(res == -1){
            res = nums.length;
        }
        
        return res;
    }
}

基于二分查找的方法

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

66. Plus One

class Solution {
    public int[] plusOne(int[] digits) {
        for(int i = digits.length - 1; i >= 0; --i){
            if(digits[i] + 1 <= 9){
                digits[i]++;
                return digits;
            }
            digits[i] = 0;
        }
        int[] res = new int[digits.length + 1];
        res[0] = 1;
        return res;
    }
}