476. Number Complement

476. Number Complement

Given a positive integer, output its complement number. The complement strategy is to flip the bits of its binary representation.

Note:
The given integer is guaranteed to fit within the range of a 32-bit signed integer.
You could assume no leading zero bit in the integer’s binary representation.
Example 1:
Input: 5
Output: 2
Explanation: The binary representation of 5 is 101 (no leading zero bits), and its complement is 010. So you need to output 2.
Example 2:
Input: 1
Output: 0
Explanation: The binary representation of 1 is 1 (no leading zero bits), and its complement is 0. So you need to output 0.

题目的意思很简单,给定一个正整数,其二进制格式中(不包含前导零),各位取反,原来是0,变成1,原来是1,变成0.这样得到一个新数,求这个新数。
题目很简单,最直接的想法是,把这个数转化为不含前导零的二进制,然后逐位取反算出结果。

方法如下:
也可以不使用数组进行保存

int findComplement(int num) {
    int bits[33], pos = 0;
    int res = 0, i;
    
    while (0 != num) {
        bits[pos++] = num & 1;
        num >>= 1;
    }
    
    for (i = 0; i < pos; ++i) {
        res += (bits[i] ^ 1) * (1UL << i);    
    }
    
    return res;
}

代码如下:

int findComplement(int num) {
    int i, res = 0;
    
    for (i = 0; i < 31; ++i) {
        if ((1UL << i) > num)break;
        if (0 == ((1UL << i) & num))
            res |= (1UL << i);
    }
    return res;
}

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本文标题:476. Number Complement

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