LeetCode | Single Number II
2014-02-14 23:44
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题目
Given an array of integers, every element appears three times except for one. Find that single one.
Note:
Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?
分析1
由于int型由32bit表示,因此可以用一个长度为32的int数组保存各个比特位上1出现的次数。最后,将数组各元素对3取余,那么32位数组就纪录了只出现了一次的整数的二进制表示。
解法1
可以用三个整数纪录32个比特位上1出现的次数,ones中比特位为1,表示该位出现了1次,twos中比特位为1,表示该位出现了2次,当某比特位出现三次后,就将ones和twos中对应比特位置为0。遍历完一遍数组后,ones即表示只出现了一次的数字。
解法2
public class SingleNumberII {
public int singleNumber(int[] A) {
if (A == null || A.length <= 0) {
return 0;
}
int ones = 0, twos = 0, threes = 0;
for (int i = 0; i < A.length; ++i) {
twos |= ones & A[i];
ones ^= A[i];
threes = ones & twos;
ones &= ~threes;
twos &= ~threes;
}
return ones;
}
}分析3
同样是利用三个整数纪录32个比特位上1出现的次数,不过方法看上去更简洁些,具体参考http://oj.leetcode.com/discuss/857/constant-space-solution。
同时,上述链接中还将该问题扩展至了:数组中所有整数都出现了k次,除了一个数只出现了l次,如何找到这个数。
解法3
public class SingleNumberII {
public int singleNumber(int[] A) {
if (A == null)
return 0;
int x0 = ~0, x1 = 0, x2 = 0, t;
for (int i = 0; i < A.length; i++) {
t = x2;
x2 = (x1 & A[i]) | (x2 & ~A[i]);
x1 = (x0 & A[i]) | (x1 & ~A[i]);
x0 = (t & A[i]) | (x0 & ~A[i]);
}
return x1;
}
}
Given an array of integers, every element appears three times except for one. Find that single one.
Note:
Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?
分析1
由于int型由32bit表示,因此可以用一个长度为32的int数组保存各个比特位上1出现的次数。最后,将数组各元素对3取余,那么32位数组就纪录了只出现了一次的整数的二进制表示。
解法1
public class SingleNumberII { private final static int INTEGER_DIGITS = 32; public int singleNumber(int[] A) { if (A == null || A.length <= 0) { return 0; } int ret = 0; int[] count = new int[INTEGER_DIGITS]; for (int i = 0; i < INTEGER_DIGITS; ++i) { for (int j = 0; j < A.length; ++j) { count[i] += (A[j] >> i) & 0x0001; } ret |= (count[i] % 3) << i; } return ret; } }分析2
可以用三个整数纪录32个比特位上1出现的次数,ones中比特位为1,表示该位出现了1次,twos中比特位为1,表示该位出现了2次,当某比特位出现三次后,就将ones和twos中对应比特位置为0。遍历完一遍数组后,ones即表示只出现了一次的数字。
解法2
public class SingleNumberII {
public int singleNumber(int[] A) {
if (A == null || A.length <= 0) {
return 0;
}
int ones = 0, twos = 0, threes = 0;
for (int i = 0; i < A.length; ++i) {
twos |= ones & A[i];
ones ^= A[i];
threes = ones & twos;
ones &= ~threes;
twos &= ~threes;
}
return ones;
}
}分析3
同样是利用三个整数纪录32个比特位上1出现的次数,不过方法看上去更简洁些,具体参考http://oj.leetcode.com/discuss/857/constant-space-solution。
同时,上述链接中还将该问题扩展至了:数组中所有整数都出现了k次,除了一个数只出现了l次,如何找到这个数。
解法3
public class SingleNumberII {
public int singleNumber(int[] A) {
if (A == null)
return 0;
int x0 = ~0, x1 = 0, x2 = 0, t;
for (int i = 0; i < A.length; i++) {
t = x2;
x2 = (x1 & A[i]) | (x2 & ~A[i]);
x1 = (x0 & A[i]) | (x1 & ~A[i]);
x0 = (t & A[i]) | (x0 & ~A[i]);
}
return x1;
}
}
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