[LeetCode][29. Divide Two Integers] 5 Approaches: Brute Force use Long, Brute Force use Int, Binary Search use Long, Binary Search use Int and Recursion

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By Long Luo

This article is the solution 5 Approaches: BF use Long, BF use Int, Binary Search use Long, Binary Search use Int and Recursion of Problem 29. Divide Two Integers , Chinese version is 3种方法：暴力法，二分搜索，递归 .

Here shows 5 Approaches to slove this problem: Brute Force use Long\texttt{Long}, Brute Force use Int\texttt{Int}, Binary Search use Long\texttt{Long}, Binary Search use Int\texttt{Int} and Recursion.

Intuition

To divide two integers without using multiplication, division, and mod operator, so we can subtract the divisor\textit{divisor} from the dividend\textit{dividend} util the result≥0\textit{result} \ge 0.

Brute Force use Long

We can make the dividend\textit{dividend} and divisor\textit{divisor} positive, and cast to long\texttt{long}, then process.

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public int divide(int dividend, int divisor) {
    if (dividend == 0) {
        return 0;
    }

    long dividendLong = dividend;
    long divisorLong = divisor;

    boolean sign = false;
    if (dividendLong < 0 && divisorLong < 0) {
        dividendLong = -dividendLong;
        divisorLong = -divisorLong;
    } else if (dividendLong < 0 && divisorLong > 0) {
        sign = true;
        dividendLong = -dividendLong;
    } else if (dividendLong > 0 && divisorLong < 0) {
        sign = true;
        divisorLong = -divisorLong;
    }

    long ans = 0;
    while (dividendLong >= divisorLong) {
        dividendLong -= divisorLong;
        ans++;
    }

    ans = sign ? -ans : ans;

    return ans > Integer.MAX_VALUE ? Integer.MAX_VALUE : (int) ans;
}

The solution will Time Limit Exceeded, we have to deal with some corner cases.

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public int divide(int dividend, int divisor) {
    if (divisor == Integer.MIN_VALUE) {
        return dividend == Integer.MIN_VALUE ? 1 : 0;
    }
    
    if (dividend == Integer.MIN_VALUE) {
        if (divisor == 1) {
            return dividend;
        } else if (divisor == -1) {
            return Integer.MAX_VALUE;
        }
    } else if (dividend == Integer.MAX_VALUE) {
        if (divisor == 1) {
            return dividend;
        } else if (divisor == -1) {
            return -dividend;
        }
    }

    long dividendLong = dividend;
    long divisorLong = divisor;

    boolean sign = false;
    if (dividendLong < 0 && divisorLong < 0) {
        dividendLong = -dividendLong;
        divisorLong = -divisorLong;
    } else if (dividendLong < 0 && divisorLong > 0) {
        sign = true;
        dividendLong = -dividendLong;
    } else if (dividendLong > 0 && divisorLong < 0) {
        sign = true;
        divisorLong = -divisorLong;
    }

    long ans = 0;
    while (dividendLong >= divisorLong) {
        dividendLong -= divisorLong;
        ans++;
    }

    ans = sign ? -ans : ans;

    return ans > Integer.MAX_VALUE ? Integer.MAX_VALUE : (int) ans;
}

Analysis

  • Time Complexity: O(x/y)O(x / y).
  • Space Complexity: O(1)O(1).

Brute Force use Int

Since the environment that could only store integers within the 32−bit32-bit signed integer, so we have to deal with it.

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class Solution {
    public int divide(int dividend, int divisor) {
        if (divisor == Integer.MIN_VALUE) {
            return dividend == Integer.MIN_VALUE ? 1 : 0;
        }

        if (dividend == 0) {
            return 0;
        }

        if (dividend == Integer.MIN_VALUE) {
            if (divisor == 1) {
                return dividend;
            } else if (divisor == -1) {
                return Integer.MAX_VALUE;
            }
        } else if (dividend == Integer.MAX_VALUE) {
            if (divisor == 1) {
                return dividend;
            } else if (divisor == -1) {
                return -dividend;
            }
        }

        int ans = 0;
        boolean sign = true;
        if (dividend > 0 && divisor > 0) {
            dividend = -dividend;
            sign = false;
        } else if (dividend > 0 && divisor < 0) {
            dividend = -dividend;
            divisor = -divisor;
        } else if (dividend < 0 && divisor < 0) {
            sign = false;
            divisor = -divisor;
        }

        while (dividend + divisor <= 0) {
            dividend += divisor;
            ans++;
        }

        return sign ? -ans : ans;
    }
}

Analysis

  • Time Complexity: O(x/y)O(x / y).
  • Space Complexity: O(1)O(1).

Binary Search use Long

Refer to
Fast Power Algorithm: Binary Exponentiation , we can use the quickAdd\texttt{quickAdd} like the quickMul\texttt{quickMul}.

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class Solution {
    public int divide(int dividend, int divisor) {
        long x = dividend;
        long y = divisor;

        boolean sign = false;

        if ((x > 0 && y < 0) || (x < 0 && y > 0)) {
            sign = true;
        }

        if (x < 0) {
            x = -x;
        }

        if (y < 0) {
            y = -y;
        }

        long left = 0;
        long right = x;

        while (left < right) {
            long mid = (left + right + 1) >> 1;
            long result = quickAdd(y, mid);
            if (result <= x) {
                left = mid;
            } else {
                right = mid - 1;
            }
        }

        long ans = sign ? -left : left;
        if (ans > Integer.MAX_VALUE || ans < Integer.MIN_VALUE) {
            return Integer.MAX_VALUE;
        }

        return (int) ans;
    }

    public long quickAdd(long x, long y) {
        long ans = 0;
        while (y > 0) {
            if ((y & 0x01) == 1) {
                ans += x;
            }

            x += x;
            y = y >> 1;
        }

        return ans;
    }
}

Analysis

  • Time Complexity: O(logx×logy)O(logx \times logy).
  • Space Complexity: O(1)O(1).

Binary Search use Int

  1. the corner cases;
  2. Record the sign of the final result and turn both numbers to negative numbers;
  3. Approximate the divisor\textit{divisor} by increasing the dividend\textit{dividend} incrementally.
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class Solution {
    public int divide(int dividend, int divisor) {
        if (divisor == Integer.MIN_VALUE) {
            return dividend == Integer.MIN_VALUE ? 1 : 0;
        }

        if (dividend == 0) {
            return 0;
        }

        if (dividend == Integer.MIN_VALUE) {
            if (divisor == 1) {
                return Integer.MIN_VALUE;
            } else if (divisor == -1) {
                return Integer.MAX_VALUE;
            }
        }

        boolean sign = false;
        if ((dividend > 0 && divisor < 0) || (dividend < 0 && divisor > 0)) {
            sign = true;
        }

        if (dividend > 0) {
            dividend = -dividend;
        }

        if (divisor > 0) {
            divisor = -divisor;
        }

        int MAX = Integer.MIN_VALUE >> 1;
        int ans = 0;

        // dividend became negative
        while (dividend <= divisor) {
            int temp = divisor;
            int step = -1;

            while (temp >= MAX && step >= MAX && temp >= dividend - temp) {
                temp += temp;
                step += step;
            }

            dividend -= temp;
            ans += step;
        }

        return sign ? ans : -ans;
    }
}

Analysis

  • Time Complexity: O(logx×logy)O(logx \times logy).
  • Space Complexity: O(1)O(1).

Recursion

The recurison method.

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class Solution {
    public int divide(int dividend, int divisor) {
        if (divisor == Integer.MIN_VALUE) {
            return dividend == Integer.MIN_VALUE ? 1 : 0;
        }

        if (dividend == 0) {
            return 0;
        }

        if (dividend == Integer.MIN_VALUE) {
            if (divisor == 1) {
                return Integer.MIN_VALUE;
            } else if (divisor == -1) {
                return Integer.MAX_VALUE;
            }
        }

        long x = dividend;
        long y = divisor;

        boolean sign = false;
        if ((x > 0 && y < 0) || (x < 0 && y > 0)) {
            sign = true;
        }

        x = x > 0 ? x : -x;
        y = y > 0 ? y : -y;

        long ans = div(x, y);
        if (ans > Integer.MAX_VALUE || ans < Integer.MIN_VALUE) {
            return Integer.MAX_VALUE;
        }

        return (int) (sign ? -ans : ans);
    }

    public long div(long dividend, long divisor) {
        if (dividend < divisor) {
            return 0;
        }

        long ans = 1;
        long temp = divisor;

        while ((temp + temp) <= dividend) {
            ans = ans << 1;
            temp = temp << 1;
        }

        return ans + div(dividend - temp, divisor);
    }
}

Analysis

  • Time Complexity: O(logx×logy)O(logx \times logy).
  • Space Complexity: O(1)O(1).

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