【LeetCode刷题日记】306. 累加数

题目

累加数 是一个字符串，组成它的数字可以形成累加序列。
一个有效的 累加序列 必须 至少 包含 3 个数。除了最开始的两个数以外，字符串中的其他数都等于它之前两个数相加的和。
给你一个只包含数字 '0'-'9' 的字符串，编写一个算法来判断给定输入是否是 累加数 。如果是，返回 true ；否则，返回 false 。

说明：累加序列里的数，除数字 0 之外，不会 以 0 开头，所以不会出现 1, 2, 03 或者 1, 02, 3 的情况。

示例 1：
输入："112358"
输出：true 
解释：累加序列为: 1, 1, 2, 3, 5, 8 。1 + 1 = 2, 1 + 2 = 3, 2 + 3 = 5, 3 + 5 = 8

示例 2：
输入："199100199"
输出：true 
解释：累加序列为: 1, 99, 100, 199。1 + 99 = 100, 99 + 100 = 199
 
提示：
1 <= num.length <= 35
num 仅由数字（0 - 9）组成

题解

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C

char * stringAdd(const char * s, int firstStart, int firstEnd, int secondStart, int secondEnd) {
    char * third = (char *)malloc(sizeof(char) * (strlen(s) + 1));
    int thirdSize = 0;
    int carry = 0, cur = 0;
    
    while (firstEnd >= firstStart || secondEnd >= secondStart || carry != 0) {
        cur = carry;
        if (firstEnd >= firstStart) {
            cur += s[firstEnd] - '0';
            --firstEnd;
        }
        if (secondEnd >= secondStart) {
            cur += s[secondEnd] - '0';
            --secondEnd;
        }
        carry = cur / 10;
        cur %= 10;
        third[thirdSize] = cur + '0';
        thirdSize++;
    }

    int left = 0;
    int right = thirdSize - 1;
    while (left < right) {
        char c = third[left];
        third[left] = third[right];
        third[right] = c;
        ++left;
        --right;
    }
    third[thirdSize] = '\0';
    return third;
}

bool valid(int secondStart, int secondEnd, const char * num) {
    int n = strlen(num);
    int firstStart = 0, firstEnd = secondStart - 1;
    while (secondEnd <= n - 1) {
        char * third = stringAdd(num, firstStart, firstEnd, secondStart, secondEnd);
        int thirdStart = secondEnd + 1;
        int thirdEnd = secondEnd + strlen(third);
        if (thirdEnd >= n || strncmp(num + thirdStart, third, thirdEnd - thirdStart + 1)) {
            free(third);
            break;
        }
        free(third);
        if (thirdEnd == n - 1) {
            return true;
        }
        firstStart = secondStart;
        firstEnd = secondEnd;
        secondStart = thirdStart;
        secondEnd = thirdEnd;
    }
    return false;
}


bool isAdditiveNumber(char * num){
    int n = strlen(num);
    for (int secondStart = 1; secondStart < n - 1; ++secondStart) {
        if (num[0] == '0' && secondStart != 1) {
            break;
        }
        for (int secondEnd = secondStart; secondEnd < n - 1; ++secondEnd) {
            if (num[secondStart] == '0' && secondStart != secondEnd) {
                break;
            }
            if (valid(secondStart, secondEnd, num)) {
                return true;
            }
        }
    }
    return false;
}

C++

class Solution {
public:
    bool isAdditiveNumber(string num) {
        int n = num.size();
        for (int secondStart = 1; secondStart < n - 1; ++secondStart) {
            if (num[0] == '0' && secondStart != 1) {
                break;
            }
            for (int secondEnd = secondStart; secondEnd < n - 1; ++secondEnd) {
                if (num[secondStart] == '0' && secondStart != secondEnd) {
                    break;
                }
                if (valid(secondStart, secondEnd, num)) {
                    return true;
                }
            }
        }
        return false;
    }

    bool valid(int secondStart, int secondEnd, string num) {
        int n = num.size();
        int firstStart = 0, firstEnd = secondStart - 1;
        while (secondEnd <= n - 1) {
            string third = stringAdd(num, firstStart, firstEnd, secondStart, secondEnd);
            int thirdStart = secondEnd + 1;
            int thirdEnd = secondEnd + third.size();
            if (thirdEnd >= n || !(num.substr(thirdStart, thirdEnd - thirdStart + 1) == third)) {
                break;
            }
            if (thirdEnd == n - 1) {
                return true;
            }
            firstStart = secondStart;
            firstEnd = secondEnd;
            secondStart = thirdStart;
            secondEnd = thirdEnd;
        }
        return false;
    }

    string stringAdd(string s, int firstStart, int firstEnd, int secondStart, int secondEnd) {
        string third;
        int carry = 0, cur = 0;
        while (firstEnd >= firstStart || secondEnd >= secondStart || carry != 0) {
            cur = carry;
            if (firstEnd >= firstStart) {
                cur += s[firstEnd] - '0';
                --firstEnd;
            }
            if (secondEnd >= secondStart) {
                cur += s[secondEnd] - '0';
                --secondEnd;
            }
            carry = cur / 10;
            cur %= 10;
            third.push_back(cur + '0');
        }
        reverse(third.begin(), third.end());
        return third;
    }
};

java

class Solution {
    public boolean isAdditiveNumber(String num) {
        int n = num.length();
        for (int secondStart = 1; secondStart < n - 1; ++secondStart) {
            if (num.charAt(0) == '0' && secondStart != 1) {
                break;
            }
            for (int secondEnd = secondStart; secondEnd < n - 1; ++secondEnd) {
                if (num.charAt(secondStart) == '0' && secondStart != secondEnd) {
                    break;
                }
                if (valid(secondStart, secondEnd, num)) {
                    return true;
                }
            }
        }
        return false;
    }

    public boolean valid(int secondStart, int secondEnd, String num) {
        int n = num.length();
        int firstStart = 0, firstEnd = secondStart - 1;
        while (secondEnd <= n - 1) {
            String third = stringAdd(num, firstStart, firstEnd, secondStart, secondEnd);
            int thirdStart = secondEnd + 1;
            int thirdEnd = secondEnd + third.length();
            if (thirdEnd >= n || !num.substring(thirdStart, thirdEnd + 1).equals(third)) {
                break;
            }
            if (thirdEnd == n - 1) {
                return true;
            }
            firstStart = secondStart;
            firstEnd = secondEnd;
            secondStart = thirdStart;
            secondEnd = thirdEnd;
        }
        return false;
    }

    public String stringAdd(String s, int firstStart, int firstEnd, int secondStart, int secondEnd) {
        StringBuffer third = new StringBuffer();
        int carry = 0, cur = 0;
        while (firstEnd >= firstStart || secondEnd >= secondStart || carry != 0) {
            cur = carry;
            if (firstEnd >= firstStart) {
                cur += s.charAt(firstEnd) - '0';
                --firstEnd;
            }
            if (secondEnd >= secondStart) {
                cur += s.charAt(secondEnd) - '0';
                --secondEnd;
            }
            carry = cur / 10;
            cur %= 10;
            third.append((char) (cur + '0'));
        }
        third.reverse();
        return third.toString();
    }
}