• 476. Number Complement


    package LeetCode_476
    
    /**
     * 476. Number Complement
     * https://leetcode.com/problems/number-complement/description/
     *
    Given a positive integer num, output its complement number. The complement strategy is to flip the bits of its binary representation.
    
    Example 1:
    Input: num = 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: num = 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.
    
    Constraints:
    The given integer num is guaranteed to fit within the range of a 32-bit signed integer.
    num >= 1
    You could assume no leading zero bit in the integer’s binary representation.
     * */
    class Solution {
        /*
        * Solution: Bit operation, Time complexity:O(32), Space complexity:O(1);
        * 5 is '00000101', because it complement number is '00000010':
        * so we need a mask like this:'11111000', then: ~num ^ mask => ~num is:'11111010' ^ mask=> the result: '00000010'
        * How i can make the mask '11111000'
        * 1.set mask: ...11111111 via ~0
        * 2.loop to left shift the mask till num & mask is '00000000'
        *
        以下是完整的位运算符(只用于Int和Long)
            shl(bits) – 有符号左移(signed shift left,相当于Java的<<)
            shr(bits) – 有符号右移(signed shift right,相当于Java的>>)
            ushr(bits) – 无符号右移(unsigned shift right,相当于Java的>>>)
            and(bits) – 按位与(bitwise and,相当于Java的&)//一一为一,其它为0
            or(bits) – 按位或(bitwise or,相当于Java的|) //有一为一,零零为0
            xor(bits) – 按位异或(bitwise xor,相当于Java的^)//相同为0,不相同为1
            inv() – 按位取反(bitwise inversion,相当于Java的~)var z = y.inv() //z是y取反获得的
        * */
        fun bitwiseComplement(N: Int): Int {
            val zero = 0
            var mask = zero.inv()//mask is ...11111111
            while ((N and mask) != 0) {
                mask = mask shl 1
            }
            return N.inv() xor mask
        }
    }
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  • 原文地址:https://www.cnblogs.com/johnnyzhao/p/13304916.html
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