91 lines
2.1 KiB
C++
91 lines
2.1 KiB
C++
// Source : https://oj.leetcode.com/problems/jump-game-ii/
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// Author : Hao Chen
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// Date : 2014-07-18
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/**********************************************************************************
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*
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* Given an array of non-negative integers, you are initially positioned at the first index of the array.
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*
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* Each element in the array represents your maximum jump length at that position.
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*
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* Your goal is to reach the last index in the minimum number of jumps.
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*
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* For example:
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* Given array A = [2,3,1,1,4]
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*
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* The minimum number of jumps to reach the last index is 2.
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* (Jump 1 step from index 0 to 1, then 3 steps to the last index.)
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*
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*
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**********************************************************************************/
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#include <iostream>
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using namespace std;
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//Acutally, using the Greedy algorithm can have the answer
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int jump(int A[], int n) {
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if (n<=1) return 0;
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int steps = 0;
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int coverPos = 0;
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for (int i=0; i<=coverPos&& i<n; ){
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if (A[i]==0) return -1;
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if(coverPos < A[i]+i){
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coverPos = A[i]+i;
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steps++;
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}
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if (coverPos >= n-1){
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return steps;
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}
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//Greedy: find the next place which can have biggest distance
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int nextPos=0;
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int maxDistance=0;
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for(int j=i+1; j<=coverPos; j++){
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if ( A[j]+j > maxDistance ) {
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maxDistance = A[j]+j;
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nextPos = j;
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}
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}
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i = nextPos;
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}
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return steps;
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}
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void printArray(int a[], int n){
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cout << "{ ";
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for(int i=0; i<n; i++){
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if(i) cout << ", ";
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cout << a[i];
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}
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cout << " } ";
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}
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int main()
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{
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#define TEST(a) printArray(a, sizeof(a)/sizeof(a[0])); cout<<jump(a, sizeof(a)/sizeof(a[0]))<<endl;
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int a1[]={0};
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TEST(a1);
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int a2[]={1};
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TEST(a2);
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int a3[]={3,2,1,0,4};
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TEST(a3);
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int a4[]={2,3,1,1,4};
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TEST(a4);
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int a5[]={1,2,3};
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TEST(a5);
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// 0 -> 1 -> 4 -> end
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int a6[]={2,3,1,1,4,0,1};
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TEST(a6);
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// 0 -> 1 -> 3 -> end
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int a7[]={2,3,1,2,0,1};
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TEST(a7);
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return 0;
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}
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