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440.cpp
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440.cpp
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__________________________________________________________________________________________________
sample 4 ms submission
class Solution {
public:
int numsToSkip(long currNum, int n){
long nextNum=currNum+1;
int total = 0;
while (currNum<=n){
if (nextNum>n){
total+=(n-currNum+1);
break;
} else {
total+=(nextNum-currNum);
currNum*=10;
nextNum*=10;
}
}
return total;
}
int findKthNumber(int n, int k) {
int currNum=1;
int numsPast = 0;
while (numsPast<(k-1)){
int skip = numsToSkip((long)currNum,n);
if (skip+numsPast<k) {
currNum++;
numsPast+=skip;
}
else {
currNum*=10;
numsPast++;
}
}
return currNum;
}
};
__________________________________________________________________________________________________
sample 8340 kb submission
class Solution {
public:
int findKthNumber(int n, int k) {
int curr = 1;
while (k > 1) {
int count = countNums(curr, n);
if (k > count) { // 走右兄弟节点
curr++;
k -= count;
} else { // 不是当前节点,走最左子节点
curr *= 10;
k--;
}
}
return curr;
}
// 以数p为根的子树含多少[1,n]间的数?
// 可累加[p,p+1)、[p *10,(p+1) *10)、[p *100,(p+1) *100)、... 与[1,n]重合的部分
int countNums(int p, long n) {
int count = 0;
long start = p, end = p + 1;
while (start <= n) {
count += min(end, n + 1) - start;
start *= 10, end *= 10;
}
return count;
}
};
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