Go Java算法之累加数示例详解

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();
    }
}

func add(a, b string) string {
    res, one := []byte{}, 0
    for i, j := len(a) - 1, len(b) - 1 ; i >= 0 || j >= 0 ; {
        curA, curB := 0, 0
        if i >= 0 {
            curA = int(a[i] - '0')
            i--
        }
        if j >= 0 {
            curB = int(b[j] - '0')
            j--
        }
        cur := curA + curB + one
        one = cur/10
        res = append(res, byte(cur%10)+'0')
    }
    if one == 1 {
        res = append(res, '1')
    }
    for i, n := 0, len(res); i < n/2; i++ {
        res[i], res[n-1-i] = res[n-1-i], res[i]
    }
    return string(res)
}
func dfs(num string, first, second int) bool {
    n, last := len(num), 0
    for second < n {
        if (num[last] == '0' && first > last + 1) || (num[first] == '0' && second > first + 1){
            return false
        }
        s := add(num[last:first], num[first:second])
        if second + len(s) > n || num[second:second + len(s)] != s {
            return false
        }
        last, first, second = first, second, second + len(s)
    }
    return true
}
func isAdditiveNumber(num string) bool {
    for i:=1;i<len(num)-1;i++ {
        for j:=i+1;j<len(num);j++{
            if dfs(num, i, j){
                return true
            }
        }
    }
    return false
}