229. Majority Element II

Moore

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class Solution {
    public List<Integer> majorityElement(int[] nums) {
        int candidate1 = 0;
        int candidate2 = 0;
        int votes1 = 0;
        int votes2 = 0;

        for (int num : nums) {
            // 注意需要先比较相等，都不相等的情况下再比较票数是否为 0, 如果先比较票数是否为 0, 则可能出现两个候选人使用同一个数字的情况
            // eg: [2, 1, 1, 3, 1, 4, 5, 6]
            if (num == candidate1) {
                votes1++;
            } else {
                if (num == candidate2) {
                    votes2++;
                } else {
                    if (votes1 == 0) {
                        candidate1 = num;
                        votes1++;
                    } else if (votes2 == 0) {
                        candidate2 = num;
                        votes2++;
                    } else {
                        votes1--;
                        votes2--;
                    }
                }
            }
        }

        int count1 = 0;
        int count2 = 0;

        for (int num : nums) {
            if (num == candidate1) {
                count1++;
            } else if (num == candidate2) {
                // 注意此处是 else if, 主要处理数组为 [0, 0] 这种情况，此时两个 candidate 值相同
                count2++;
            }
        }

        List<Integer> list = new ArrayList<>();
        if (count1 > nums.length / 3) {
            list.add(candidate1);
        }
        if (count2 > nums.length / 3) {
            list.add(candidate2);
        }
        return list;
    }
}

Moore

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class Solution {
    public List<Integer> majorityElement(int[] nums) {
        int candidate1 = 0;
        int candidate2 = 0;
        int votes1 = 0;
        int votes2 = 0;

        for (int num : nums) {
            if (num == candidate1) {
                votes1++;
                continue;
            }
            if (num == candidate2) {
                votes2++;
                continue;
            }

            if (votes1 == 0) {
                candidate1 = num;
                votes1++;
                continue;
            }
            if (votes2 == 0) {
                candidate2 = num;
                votes2++;
                continue;
            }

            votes1--;
            votes2--;
        }

        int count1 = 0;
        int count2 = 0;

        for (int num : nums) {
            if (num == candidate1) {
                count1++;
            } else if (num == candidate2) {
                count2++;
            }
        }

        List<Integer> list = new ArrayList<>();
        if (count1 > nums.length / 3) {
            list.add(candidate1);
        }
        if (count2 > nums.length / 3) {
            list.add(candidate2);
        }
        return list;
    }
}

References

229. Majority Element II