算法练习(4):牛客在线编程05 哈希

package jz.bm;

import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;

public class bm5 {
    /**
     * BM50 两数之和
     */
    public int[] twoSum (int[] numbers, int target) {
        int[] res = new int[2];
        HashMap<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < numbers.length; i++) {
            if (map.containsKey(target - numbers[i])) {
                res[0] = map.get(target - numbers[i]) + 1;
                res[1] = i + 1;
                return res;
            } else {
                map.put(numbers[i], i);
            }
        }
        return res;
    }

    /**
     * BM51 数组中出现次数超过一半的数字
     */
    public int MoreThanHalfNum_Solution(int [] array) {
        HashMap<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < array.length; i++) {
            if (map.containsKey(array[i])) {
                map.put(array[i], map.get(array[i]) + 1);
            } else {
                map.put(array[i], 1);
            }
            if (map.get(array[i]) > array.length / 2) {
                return array[i];
            }
        }
        return array[0];
    }

    /**
     * BM52 数组中只出现一次的两个数字
     */
    public int[] FindNumsAppearOnce (int[] array) {
        int[] res = new int[2];
        HashMap<Integer, Integer> map = new HashMap<>();
        for (int k : array) {
            if (map.containsKey(k)) {
                map.put(k, 2);
            } else {
                map.put(k, 1);
            }
        }
        ArrayList<Integer> list = new ArrayList<>();
        for (int j : array) {
            if (map.get(j) == 1) {
                list.add(j);
            }
        }
        res[0] = Math.min(list.get(0), list.get(1));
        res[1] = Math.max(list.get(0), list.get(1));
        return res;
    }

    /**
     * BM53 缺失的第一个正整数
     */
    public int minNumberDisappeared (int[] nums) {
        Arrays.sort(nums);
        HashMap<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            map.put(nums[i], i);
        }
        for (int i = 1; i < Integer.MAX_VALUE; i++) {
            if (!map.containsKey(i)) {
                return i;
            }
        }
        return -1;
    }

    /**
     * BM54 三数之和
     */
    public ArrayList<ArrayList<Integer>> threeSum(int[] num) {
        ArrayList<ArrayList<Integer>> lists = new ArrayList<>();
        Arrays.sort(num);
        HashMap<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < num.length; i++) {
            map.put(num[i], i);
        }
        int a, b, c;
        for (int i = 0; i < num.length; i = map.get(a) + 1) {
            a = num[i];
            for (int j = i + 1; j < num.length; j = map.get(b) + 1) {
                b = num[j];
                c = -a - b;
                if (map.containsKey(c) && map.get(c) > j) {
                    ArrayList<Integer> list = new ArrayList<>();
                    list.add(a);
                    list.add(b);
                    list.add(c);
                    lists.add(list);
                }
            }
        }
        return lists;
    }
}

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